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ELEMENTS 


OF 


SANITARY  ENGINEERING. 


BY 

MANSFIELD    MERRIMAN, 

MEMBER  OF  AMERICAN  SOCIETY  OF  CIVIL  ENGINEERS. 
FOURTH  EDITION,   REVISED 

WITH  THE  ASSISTANCE  OF 

RICHARD    M.  MERRIMAN, 

ASSOCIATE  MEMBER  OF  AMERICAN  SOCIETY  OF  CIVIL  ENGINEERS. 


TOTAL  JS2UE/FWE  >THOUSANlV 

*        •»"*•»**%        ^  * 


NEW  YORK 

JOHN   WILEY   &   SONS,    INC. 
LONDON:  CHAPMAN  &  HALL,  LIMITED 
1918 


.Copyright,  1898. 1906,  1918, 

BY 
MANSFIELD    MERRIMAN. 


PRESS  OF 

BRAUNWORTH  li  CO. 

BOOK  MANUFACTURERS 

BROOKLYN,  N.  V. 


PREFACE  TO  THIRD  EDITION. 


While  this  volume  is  primarily  intended  for  the  use  of  students 
in  engineering  colleges,  its  plan  and  arrangement  are  materially 
different  from  those  of  other  text-books  on  water  supply  and  sew- 
erage. The  effort  has  been  made  to  present  the  subject  clearly 
and  concisely  in  the  smallest  possible  space,  giving  greater  prom- 
inence to  fundamental  principles  than  to  details  of  construction 
and  operation.  It  is  also  hoped  that  the  book  may  prove  useful 
to  municipal  officers  who  have  supervision  of  sanitary  works  as 
well  as  to  the  public  in  general,  for  it  presents  the  guiding  princi- 
ples which  should  be  observed  in  order  to  secure  a  pure  water 
supply  or  an  efficient  system  of  sewerage. 

At  the  end  of  each  chapter  are  given  exercises  and  problems 
for  students.  These  require  that  the  student  shall  consult  cyclo- 
pedias, books,  and  engineering  literature  in  order  to  obtain 
information  regarding  the  details  of  special  topics  or  of  the  con- 
struction of  plants.  It  will  be  found  highly  advantageous  to  have 
several  of  these  exercises  presented  and  discussed  at  every  class 
recitation,  each  being  presented  by  a  different  student  while  the 
class  takes  notes  and  joins  in  the  discussion.  In  this  way  each 
student  will,  during  the  course,  become  acquainted  with  engineer- 
ing indexes,  books,  and  journals,  and  learn  how  to  use  them  in 
finding  the  assigned  topics,  while  the  oral  presentation  of  the 
facts  and  conclusions  to  the  class  gives  him  valuable  training. 
Moreover,  it  has  been  the  experience  of  the  author  that  the  class 


382060 


. 

, 

2 
1  PREFACE. 

takes  a  far  greater  interest  in  the  subject  and  derives  a  greater 
advantage  from  a  Course  conducted  in  this  way  than  under  the 
old  plan  of  formal  questions  and  recitations  supplemented  by 
remarks  of  the  instructor. 

Since  the  publication  of  the  first  edition  of  this  book  in  1898, 
many  important  advances  in  sewage  disposal  have  been  made, 
especially  in  the  development  of  the  septic  tank,  the  contact  bed, 
and  the  sprinkling  filter.  Accordingly,  the  last  chapter  of  the 
former  editions  has  been  rewritten  and  expanded  into  two 
chapters,  one  treating  of  the  disposal  of  sewage  and  the  other  of 
the  disposal  of  refuse  and  garbage.  Changes  have  also  been 
made  in  the  other  chapters  in  order  to  bring  them  up  to  date,  and 
an  appendix  has  been  added  giving  information  regarding  a  few 
of  the  most  important  works  recently  constructed  or  now  in 
progress.  Compared  with  the  last  edition  the  number  of  pages 
has  been  increased  from  222  to  252,  and  the  number  of  exercises 
and  problems  from  1 21  to  1 58.  It  has  been  the  aim  of  the  author 
to  present  the  subject  in  such  a  manner  that  public  interest  in 
sanitary  work  may  be  increased  and  sound  engineering  education 
be  promoted. 

NOTE  TO  FOURTH  EDITION. 

In  this  edition  all  known  errors  have  been  corrected  and  some 
former  statements  and  problems  replaced  by  others  more  up  to 
date.  Art.  690  on  the  Imhoff  Tank  and  Art.  jia  on  Other  Methods 
of  Sewage  Purification  are  new.  Additional  new  matter  will  be 
found  in  Arts.  4,  25,  27,  28,  40,  55,  60,  68,  71,  82,  and  83,  several 
of  which  have  been  entirely  rewritten.  Fourteen  new  pages  of 
text  have  been  added  and  a  number  of  new  problems  and  exercises 
introduced.  These  changes  have  been  made  in  order  to  keep 
the  book  abreast  with  modern  progress  and  to  better  adapt  it  to  the 
use  of  engineers  and  students. 


CONTENTS. 

CHAPTER  I. 
SANITARY  SCIENCE. 

PAGE 

ART.     i.     INTRODUCTION.       7,V^>^  ;-'•'     '»'•      •        •  •    '  7" 

2.  HISTORICAL  NOTES  .         .        .        .        .        .  9 

3.  CLASSIFICATION  OF  DISEASES  .         .      '  »        .   <  .     12 

4.  STATISTICS  OF  MORTALITY     >.  :  .  lv-     .        .  .     15 

5.  BACTERIOLOGY.      "•'•£  -'V>£--v  "*•  ••*  .'•' '•  •' 'V  -,  .18 

6.  ORGANIC  MATTER    .       V       .'   ;     .         .        .  .21 

7.  FILTH  AND  DISEASE      ''•'.>;.     V        .       =.;* '.' •:  ...  ..  .     23 

8.  IMPURE  AIR  AND  DISEASE      .        .        .        .  <  .     25 

9.  DRINKING  WATER  AND  DISEASE     .        vc<  ..   .  .     28 

10.  MATTER  IN  NATURAL  WATERS       .        vri     .  .     30 

11.  CHEMICAL  ANALYSIS  OF  WATER      .       :*   -     .  .33 

12.  BIOLOGICAL  ANALYSIS  OF  WATER  .        .        .  .36 

13.  INTERPRETATION  OF  ANALYSES       ,;       . '•  -     .  .     39 

14.  RESULTS  OF  SANITARY  SCIENCE     '.-       .    .  .'.   .  .     42 

15.  EXERCISES  AND  PROBLEMS       *•'     J  '     .        .  .     44 

CHAPTER  II. 

WATER   AND    ITS    PURIFICATION. 

ART.  16.     THE  RAINFALL     '   ^        .;     "•,         .        .        .  .47 

17.  EVAPORATION,  RUN-OFF,  AND  PERCOLATION  .  .51 

18.  RAIN  WATER    .     T,        .        ^        .        .  .  .52 

19.  SURFACE  WATERS          •_  * '.      .        .        .  .  •     54 

20.  GROUND  WATERS     .        .        .        .        .  .  •     57 

21.  RESERVOIRS      .  60 


4  CONTENTS. 

PAGR 

ART.  22.  SEDIMENTATION  AND  AERATION     .                        .63 

23.  NATURAL  FILTRATION 66 

24.  ARTIFICIAL  METHODS  OF  PURIFICATION      .  .        .68 

25.  CHEMICAL  AND  ELECTRICAL  METHODS  .        .        .70 

26.  SCREENS  AND  STRAINERS      .  .        ,        ,'       .        .     72 

27.  MECHANICAL  FILTERS      .-       .        .        .        .         -74 

28.  SLOW  SAND  FILTRATION^.     -:  .        .        .        .         .77 

29.  OPERATION  OF  FILTER  BEDS  .  .        .        .80 

30.  EXERCISES  AND  PROBLEMS      ...        .        .        .     84 

CHAPTER  III. 
WATER-SUPPLY   SYSTEMS. 

ART.  31.  CLASSIFICATION        ..,.•'.        .        .86 

32.  CONSUMPTION  OF  WATER 89 

33.  CAPACITY  OF  STORAGE  RESERVOIRS         .        .         -91 

34.  RESERVOIR  DAMS  OF  EARTH 94 

35.  RESERVOIR  DAMS  OF  MASONRY       .        .        .         -97 

36.  WASTE-WEIRS  AND  PIPE  CONNECTIONS   .        .         .  101 

37.  AQUEDUCTS      ,        .        .     -.        .    ;     ..       .        .  103 

38.  PIPE  LINES      .        .  ,"  ..        .        .        .        .  107 

39.  DISTRIBUTING  RESERVOIRS      .        .        .        .         .no 

40.  PUMPS  AND  PUMPING 113 

41.  PUMPING  ENGINES 116 

42.  PUMPING  TO  RESERVOIRS         .        .        .       -.        .120 

43.  DIRECT  PUMPING     .        .        .        .        .        ."        .  122 

44.  TANKS  AND  STAND  PIPES       .        .        .        .        .126 

45.  STREET  MAINS  AND  FIRE  SERVICE         .        ^        .129 

46.  WATER  METERS  AND  HOUSE  PIPES        .        .        .  132 

47.  EXERCISES  AND  PROBLEMS       .....  135 

CHAPTER  IV. 
SEWERAGE   SYSTEMS. 

ART.  48.  HISTORICAL  NOTES.         .        .        .        .        .        .  139 

49.  HOUSE  FIXTURES 143 

50.  HOUSE  DRAINAGE '-,-     .  146 


CONTENTS. 


ART.  51. 

CLASSIFICATION  OF  SYSTEMS   .     '.*)','      . 

PAGE 
.      149 

52- 

.     152 

53- 

THE  SEPARATE  SYSTEM  .         .       '.        •        . 

.      156 

54- 

SIZES  OF  SEWERS     '..        ,      •  .        .        •        • 

•  J59 

55- 

CONSTRUCTION  OF  SEWERS 

.  162 

56. 

VENTILATION  AND  CLEANING  .... 

.  165 

57- 

PUMPING  OF  SEWAGE       .      •  v       .        . 

.  168 

5*. 

VACUUM  SYSTEMS    .        .  ;     *_       . 

.  170 

59- 

THE  COMPRESSED-AIR  SYSTEM         .         .        . 

•  173 

60. 

•  J75 

61. 

.  178 

CHAPTER  V. 

DISPOSAL   OF    SEWAGE. 

ART.  62. 

SEWAGE  AND  ITS  DECOMPOSITION        .       .       . 

.  180 

63- 

DISPOSAL  OF  SEWAGE  IN  RIVERS 

.  182 

64. 

SCREENING  OF  SEWAGE        .        .        . 

•  185 

65- 

.  187 

66. 

CHEMICAL  PRECIPITATION     

.  188 

67. 

INTERMITTENT  FILTRATION   

.  194 

68. 

BROAD  IRRIGATION       . 

.  198 

69. 

690. 

.  205 

70. 

2050 

71- 

lie. 

OTHER  METHODS  OF  PURIFICATION 

2ogb 

72. 

COMPARISON  OF  METHODS                        .        . 

.    211 

73. 

.    214 

CHAPTER    VI. 

REFUSE    AND    GARBAGE. 

ART.  74. 

PRIVIES  AND  CESSPOOLS  .        .        •       •       • 

.    215 

75- 

HOUSE  AND  STREET  REFUSE            •       •       • 

.    219 

76. 

CONTENTS. 


PACE 

ART.  77. 

78. 

79- 

,  228 

80. 

•  231 

81. 

•  233 

APPENDIX. 

ART.  82. 

NEW  WATER  SUPPLY  FOR  NEW  YORK  CITY 

•  235 

83- 

WATER  FILTRATION  AT  PHILADELPHIA 

.  237 

84. 

WATER  FILTRATION  AT  LITTLE  FALLS,  N.  J. 

.  234 

85- 

THE  CHICAGO  DRAINAGE  CANAL 

.    240 

86. 

BRITISH  COMMISSIONS  ON  SEWAGE  DISPOSAL 

.    241 

*!• 

.    242 

•    245 

ELEMENTS  OF  SANITARY  ENGINEERING. 


CHAPTER    I. 

SANITARY   SCIENCE. 

1  i 

1.  INTRODUCTION. 

Sanitary  science  embraces  those  principles  and  methods  by 
which  the  health  of  a  community  is  promoted  and  the  spread 
of  disease  is  prevented.  Hygiene  properly  relates  to  the 
individual  or  to  the  family,  but  sanitary  science  has  a  wider 
scope  and  includes  the  village,  the  city,  and  the  community 
at  large.  Hygiene  is  the  preservation  of  the  health  of  the 
individual  under  the  rules  of  the  physician,  while  sanitary 
science  has  for  its  aim  the  preservation  and  protection  of  the 
health  of  the  community  under  the  combined  action  of 
physicians,  engineers,  and  the  civil  authorities. 

The  field  of  sanitary  science  is  a  wide  one.  It  includes  the 
collection  of  vital  statistics,  and  particularly  the  statistics  of 
mortality  and  disease,  the  isolation  and  quarantine  of  infec- 
tious diseases,  the  disinfection  of  houses,  the  management  of 
hospitals,  and  the  proper  burial  of  the  dead.  It  embraces  all 
the  regulations  for  preventing  adulteration  of  food  and  pollu- 
tion of  air  or  water.  It  treats  of  the  methods  of  heating  and 
ventilating  public  buildings  so  as  to  promote  comfort  and 
health,  of  the  methods  for  securing  pure  and  abundant  sup- 
plies of  water,  of  the  drainage  of  land,  and  of  the  removal  of 

7 


8  SANITARY   SCIENCE.  I. 

garbage  and  sewage.  To  properly  coordinate  all  these  sub- 
jects, sanitary  science  uses  the  principles  of  biology,  chemistry, 
medicine,  physics,  and  engineering,  and  from  these  it  frames 
regulations  to  be  enforced  by  the  civil  authorities.  It  invokes 
the  science  of  the  biologist  and  chemist,  the  experience  of  the 
physician,  the  constructive  talent  of  the  engineer,  and  the 
authority  of  the  legislature  in  order  to  preserve  and  protect 
the  health  of  the  community. 

In  this  chapter  only  a  small  part  of  the  field  of  sanitary 
science  can  be  discussed,  and  the  portions  to  be  selected  are 
those  which  are  most  directly  applicable  to  the  work  of  the 
sanitary  engineer.  The  engineer  cannot  be  a  biologist  or  a 
chemist,  but  he  must  be  able  to  understand  the  main  reasons 
for  their  conclusions.  He  cannot  be  a  physician,  but  he 
should  know  something  about  the  general  subject  of  the 
prevention  of  disease.  He  cannot  be  skilled  in  architecture, 
but  he  should  understand  the  fundamental  principles  relating 
to  heating  and  ventilating.  He  cannot  be  an  expert  in  social 
science  or  in  law,  but  he  should  not  be  ignorant  of  the 
methods  by  which  vital  statistics  are  collected  and  sanitary 
regulations  are  enforced.  This  chapter  aims  to  briefly  explain 
some  of  these  subjects,  in  order  that  the  student  may  obtain 
a  broad  view  of  the  whole  field,  and  that  the  engineer  may  be 
better  able  to  effectively  cooperate  with  the  other  professions 
in  advancing  the  sanitary  condition  of  the  community. 

Civil  Engineering  is  the  art  of  economic  construction,  that 
is,  the  art  of  making  structures  for  the  public  use  at  the 
minimum  cost  for  installation  and  operation.  A  person  not 
an  engineer  may  construct  a  railroad  or  a  water-supply  system, 
but  its  cost  will  be  higher  and  its  efficiency  lower  than  one 
built  by  the  engineer  of  experience.  The  engineer,  accord- 
ing to  the  definition  of  Telford,  utilizes  the  materials  and 
forces  of  nature  for  the  benefit  of  man,  but  to  this  should  be 
added  that  in  so  doing  he  aims  to  secure  the  least  possible 
cost  of  construction  and  maintenance. 


2.  HISTORICAL   NOTES.  9 

Sanitary  engineering  is  that  branch  of  civil  engineering  which 
is  concerned  with  constructions  for  promoting  the  health  of  the 
community.  These  fall  into  three  classes,  Water  Supply, 
Sewerage,  and  Disposal  of  Refuse  and  Garbage,  and  form  the 
subjects  of  the  following  chapters.  A  pure  and  abundant  water 
supply,  an  efficient  system  of  sewerage,  and  the  proper  removal 
of  refuse  and  garbage  have  been  universally  found  to  promote 
cleanliness  and  prevent  the  spread  of  disease ;  to  provide  for 
these  in  an  economical  manner  is  the  main  work  of  the  sanitary 
engineer. 

2.  HISTORICAL  NOTES. 

The  oldest  sanitary  code  on  record  is  that  given  in  the  book 
of  Leviticus  for  the  guidance  of  the  Israelites  while  traveling 
in  the  Arabian  deserts;  the  date  of  this  code  is  about  1490 
B.C.  It  includes  rules  regarding  the  kinds  of  meat  to  be 
eaten,  the  degrees  of  consanguinity  within  which  marriages 
were  forbidden,  the  inspection  and  isolation  of  unclean  or 
diseased  persons,  and  particularly  of  lepers,  but  it  gives  no 
directions  regarding  the  purity  of  the  water  supply  or  the 
removal  of  garbage  and  refuse.  Nevertheless,  it  is  thought 
by  many  that  the  strict  observance  of  this  sanitary  code  has 
been  one  of  the  .causes  of  the  remarkable  vitality  of  the 
Jewish  race. 

The  Moabite  stone  which  records  the  rebellion  of  Mesha, 
king  of  Moab,  against  the  Israelites,  about  900  B.C.,  states 
that  Mesha  built  two  conduits  and  ordered  the  inhabitants  of 
the  city  of  Karcha  to  place  a  cistern  in  each  house.  Prior 
to  this  the  Egyptians  had  built  reservoirs  and  canals  for 
the  purpose  of  irrigation.  Nebuchadnezzar  also  constructed 
reservoirs  and  canals  near  Babylon  about  590  B.C.  Jerusalem 
had  a  water  supply  furnished  by  subterranean  aqueducts, 
some  of  which  are  yet  in  operation. 

The  Romans  at  first  built  canals  for  drainage  and  irrigation, 
and  later  constructed  extensive  systems  of  aqueducts  for  the 


10  SANITARY    SCIENCE.  I. 

water  supply  of  Rome  and  other  cities.  The  aqueducts  of 
Rome  in  97  A.D.  were  described  by  Frontinus,  a  military 
engineer,  who  was  then  the  imperial  water  commissioner; 
these  included  30  miles  of  conduits  built  on  arches  and  220 
miles  under  the  surface  of  the  ground,  and  later  there  were 
fourteen  aqueducts  having  an  aggregate  length  of  359  miles. 
It  has  been  frequently  stated  that  these  aqueducts  delivered 
to  Rome  about  300  million  gallons  of  water  per  day,  or,  since 
the  population  of  the  city  was  nearly  one  million,  about  300 
gallons  per  person  per  day.  A  recent  discussion  by  Herschel 
indicates,  however,  that  this  figure  is  much  too  high,  and  that 
probably  the  average  daily  supply  within  the  city  was  not  far 
from  50  American  gallons  per  person.  Even  this  quantity 
was  a  liberal  supply  for  domestic  and  public  use. 

After  the  division  of  the  Roman  empire,  about  300  A.D., 
and  the  subsequent  conquests  by  the  barbarians,  the  splendid 
roads  and  aqueducts  were  suffered  to  fall  into  decay,  and 
Europe  for  more  than  a  thousand  years  was  pervaded  by 
intellectual  and  social  darkness.  Unfortunately  the  teachings 
and  practice  of  the  Christian  church  during  this  period 
regarded  cleanliness  as  one  of  the  luxuries  which  was  incon- 
sistent with  godliness,  while  bodily  filth  was  considered  as  a 
mark  of  inward  piety  and  holy  sanctification.  The  example 
set  by  the  monastic  orders  was  imitated  by  the  people  at 
large;  bathing  was  unknown,  houses  and  clothing  were  filthy, 
and  the  streets  served  as  receptacles  for  garbage  and  human 
excreta.  The  result  of  this  violation  of  sanitary  principles 
is  seen  in  the  horrible  pestilences  that  spread  over  Europe. 
One  of  these,  called  the  Black  Death,  is  said  to  have  had 
40  ooo  ooo  victims  since  its  first  appearance  in  the  fourteenth 
century.  At  this  time  the  common  people  lived  in  a  manner 
more  revolting  than  that  of  barbarous  tribes  at  the  present 
day ;  oppressed  by  the  lords  and  by  the  clergy,  they  had  few 
civil  rights,  no  liberty  of  thought,  and  their  minds  were 
actuated  by  the  grossest  superstitions. 


2.  HISTORICAL  NOTES.  II 

The  revival  of  learning,  the  invention  of  printing,  and  the 
discovery  of  America  characterized  the  close  of  the  fifteenth 
century  and  led  the  way  for  the  religious  reformation  of  the 
sixteenth.  Then  ensued  that  struggle  for  liberty  of  thought 
and  freedom  of  conscience  which  is  not  yet  entirely  ended. 
Later  the  study  of  the  laws  of  nature  began  slowly  to  banish 
superstition  and  to  show  that  disease  and  pestilence  were  not 
punishments  arbitrarily  sent  from  heaven,  but  that  they 
resulted  from  man's  own  neglect  of  sanitary  principles. 
Harvey  in  1619  discovered  the  facts  regarding  the  circulation 
of  blood  in  the  veins  and  arteries,  but  it  was  not  until  after 
the  discovery  of  oxygen  by  Priestley,  in  1774,  that  the 
phenomena  could  be  fully  understood.  Medical  science 
slowly  outgrew  its  superstitions  and  began  to  found  its 
methods  of  treating  disease  upon  observed  facts  rather  than 
upon  arbitrary  fancies.  How  slow  the  progress  had  been 
from  the  fifteenth  to  the  close  of  the  eighteenth  century  may 
be  judged  from  the  fact  that  when  Jenner,  in  1798,  announced 
his  discovery  of  vaccination  as  a  preventive  of  smallpox 
both  physicians  and  clergy  almost  unanimously  denounced 
and  derided  him  in  the  strongest  language. 

During  the  first  quarter  of  the  nineteenth  century  the 
essential  elements  of  railroad  locomotion  were  perfected, 
thereby  greatly  increasing  traffic  and  commerce,  and  an  era 
of  material  progress  was  inaugurated  which  was  highly  con- 
ducive to  the  development  of  science.  Physics,  chemistry, 
and  biology  began  to  be  studied  from  a  new  point  of  view, 
and  all  the  various  subjects  which  are  now  embraced  in  the 
art  of  engineering  began  to  receive  zealous  attention.  Road 
improvements,  the  drainage  of  towns,  and  the  construction  of 
water  supplies  began.  Drains  to  carry  off  the  rainfall  had 
been  built  in  London  during  the  seventeenth  century,  but  it 
was  not  until  1815  that  they  were  allowed  to  be  used  to  carry 
away  sewage;  before  the  middle  of  the  century,  however,  a 
great  change  of  opinion  had  occurred,  and  in  1847  ft  was 


12  SANITARY   SCIENCE.  1. 

compulsory  to  turn  all  sewage  into  such  drains  or  sewers. 
At  this  date  modern  sanitary  engineering  may  be  said  to  have 
had  its  origin,  although  it  was  not  until  many  years  later  that 
the  term  became  known  to  the  public.  The  progress  that 
has  been  made  since  that  time  will  be  recorded  in  the  follow- 
ing pages  under  the  several  subdivisions  of  the  subject. 

3.  CLASSIFICATION  OF  DISEASES. 

The  ancient  idea  regarding  disease  seems  to  have  been  that 
health  was  the  normal  state  of  man,  and  that  disease  was  a 
punishment  inflicted  by  an  arbitrary  divine  authority.  Later 
this  idea  became  modified  so  as  to  regard  disease  as  the  result 
of  the  violation  of  sanitary  laws,  health  being  still  considered 
as  the  normal  condition.  This  point  of  view  is  still  not 
uncommon,  and  such  terms  as  "  preservation  of  health  "  and 
"  protection  from  disease  "  tend  to  imply  that  it  is  a  correct 
one.  Strictly  speaking,  however,  health  is  an  ideal  state,  but 
not  a  normal  state.  The  normal  or  natural  conditions  of  life 
on  this  earth  are  those  of  disease.  We  are  born  with  con- 
stitutional weaknesses  inherited  from  our  ancestors;  our  food, 
water,  and  air  contain  poisons;  extremes  of  cold  and  heat 
prevent  ideal  growth ;  infectious  germs  and  injurious  insects 
are  continually  making  attacks  on  us;  in  short,  life  is  a 
struggle  for  existence.  These  influences  are  particularly 
powerful  in  childhood,  and  statistics  show  that  over  one-fourth 
of  all  deaths  are  those  of  infants  under  one  year  of  age.  Of 
all  animals,  man  is  the  most  helpless  at  birth,  and  it  is  safe  to 
say  that  without  the  watchful  care  of  parents  or  friends  very 
few  children  could  survive  for  one  year,  even  if  suitable  food 
were  at  hand. 

It  therefore  appears  that  health  should  not  be  regarded  as 
the  normal  state  of  man  under  natural  conditions,  but  rather 
as  an  ideal  state  which  might  occur  under  ideal  conditions. 
Disease,  in  strictness,  is  to  be  regarded  as  the  normal  state. 


3.  CLASSIFICATION   OF  DISEASES.  13 

and  health  as  the  state  insured  by  eternal  vigilance  in  remov- 
ing the  causes  that  continually  tend  to  produce  disease  and 
death. 

Disease  in  general  may  be  defined  as  a  derangement  of 
the  organs  or  tissues  of  the  body  whereby  their  functions 
cannot  be  properly  performed.  Deaths  by  violence  or  acci- 
dent, those  of  women  in  childbirth,  those  of  children  due  to 
teething,  and  those  resulting  from  starvation,  excessive  labor, 
and  old  age  need  not  here  be  considered.  Local  diseases, 
such  as  those  of  the  brain  and  heart,  and  those  of  the  diges- 
tive, circulatory  and  generative  systems,  together  with  so-called 
constitutional  diseases  like  rheumatism  and  cancer  constitute 
a  large  proportion  of  all  ailments,  but  their  prevention  is  the 
province  of  the  physician  under  the  rules  of  hygiene. 

Zymotic  diseases  are  those  caused  by  infection  from  one 
person  to  another,  and  they  usually  have  a  period  of  incuba- 
tion, followed  by  illness  with  fever  and  perhaps  accompanied 
by  eruption.  Among  these  are  smallpox,  measles,  diphtheria, 
whooping-cough,  scarlet  fever,  influenza,  malaria,  typhoid 
fever,  cholera,  and  yellow  fever.  Common  colds  are  now 
understood  to  be  zymotic  diseases.  Syphilis,  gangrene,  and 
hydrophobia,  although  allied  to  the  zymotic  class,  are  generally 
called  enthetic  or  inoculated  diseases.  Tuberculosis  was 
formerly  regarded  as  a  local  constitutional  disease,  but  it  is 
now  recognized  as  zymotic  in  the  sense  that  it  is  caused  by 
infection,  hereditary  tendencies  merely  rendering  its  develop- 
ment more  rapid  in  some  individuals  than  in  others.  It  is  one 
of  the  important  aims  of  sanitary  science  to  abolish  these  dis- 
eases by  removing  their  causes.  ; 

Zymotic  diseases  are  propagated  by  the  transfer  of  living 
organic  germs  from  diseased  to  healthy  persons,  each  disease 
having  its  specific  germ.  Germs  of  yellow  fever  are  carried  from 
an  infected  to  a  healthy  person  by  mosquitoes,  being  directly 
introduced  into  the  blood  through  the  bite  of  the  insect.  Germs 


14  SANITARY   SCIENCE.  I. 

of  typhoid  fever  are  usually  brought  to  a  well  person  by  dfink- 
ing  water  which  has  been  fouled  by  the  excretions  of  persons 
ill  with  this  disease,  but  sometimes  they  are  brought  by  con- 
taminated milk,  oysters,  and  vegetables,  or  even  by  flies. 
Although  the  number  of  germs  thus  introduced  into  a  human 
body  may  be  small,  they  feed  upon  the  tissues  and  rapidly 
increase  in  number,  secreting  poisons  which  give  rise  to  the 
fever  and  other  symptoms  of  the  disease.  A  person  is  effect- 
ively guarded  against  zymotic  diseases  by  preventing  their 
specific  germs  from  entering  his  body. 

Zymotic  or  germ  diseases  are  said  to  be  contagious  or  in- 
fectious, the  first  word  implying  touch  or  contact  between  a 
healthy  and  an  ill  person,  while  the  second  implies  that  the 
infection  may  be  communicated  without  direct  contact.  Thus, 
measles  and  scarlet  fever  are  both  contagious  and  infectious, 
but  syphilis  and  smallpox  are  usually  contagious  and  not  in- 
fectious. The  word  contagious  is,  however,  often  used  as 
meaning  infectious. 

An  endemic  disease  is  one  peculiar  to  a  certain  locality,  or 
one  which  appears  regularly  at  such  localities.  For  instance, 
in  certain  mountains  of  Europe  large  numbers  pf  people  are 
afflicted  with  goitre;  in  some  low  lands  malaria  is  always 
found;  again,  at  some  tropical  seaports  yellow  fever  may  be 
expected  to  appear  regularly  in  certain  months  of  the  year. 

An  epidemic  disease  is  one  that  spreads  over  a  community 
at  irregular  intervals  and  then  for  the  most  part  disappears. 
Smallpox  was  formerly  one  of  the  best  examples  of  an 
epidemic  disease,  but  it  is  now  kept  under  control  by  vacci- 
nation and  isolation,  so  that  few  epidemics  occur  in  civilized 
countries.  Measles,  whooping-cough,  and  other  diseases  of 
childhood  often  become  epidemic  in  a  town  or  city.  Typhoid 
fever  is  one  of  the  most  dangerous  of  the  epidemic  diseases, 
its  spread  being  largely  due  to  germs  which  have  infected  the 
water  supply.  Diphtheria  is  epidemic  in  neighborhoods,  but 
not  generally  over  large  areas.  The  prevention  of  dangerous 


4.  STATISTICS   OF   MORTALITY.  1 5 

epidemics  of  zymotic  diseases  has  been  one  of  the  great  sani- 
tary triumphs  of  the  nineteenth  century.  Epidemics  of  small- 
pox, yellow  fever,  and  cholera  caused  great  devastation  in 
America  a  hundred  years  ago;  now  they  are  under  full  con- 
trol and  their  spread  is  no  longer  feared. 

4.  STATISTICS  OF  MORTALITY. 

Statistics  of  births,  marriages,  and  deaths  are  absolutely 
necessary  for  the  study  of  social  and  economic  science.  The 
record  of  deaths,  with  statement  of  the  causes  of  death,  is 
equally  necessary  for  the  successful  progress  of  sanitary 
science.  All  large  cities,  many  towns,  and  some  states  now 
require  such  a  registration,  while  medical  societies  and  hospi- 
tals are  doing  most  excellent  work  in  collecting  records  of 
illness  and  recovery.  The  mortality  statistics  collected  by  the 
enumerators  at  the  decennial  censuses  of  the  United  States  are 
defective  in  omitting  many  deaths,  and  a  satisfactory  determi- 
nation of  the  average  death  rate  for  the  entire  country  can  only 
be  made  by  comparing  the  census  returns  with  the  records  of 
the  registration  states  and  cities.  The  percentage  of  the  total 
population  included  in  the  registration  area  was,  for  1890, 
31.4  per  cent;  for  1900,  40.5  per  cent;  for  1910,  58.3  per 
cent;  and  for  1915,  67. 1  per  cent.  The  use  of  a  standard  form 
of  certificate  for  reporting  deaths  is  now  general  over  the 
registration  area,  and  it  is  to  be  hoped  that  all  states  will 
have  an  effective  system  of  registration  before  the  census  of 
1920  is  taken. 

To  obtain  correct  mortality  statistics  it  is  necessary  that 
the  law  should  require,  under  a  heavy  penalty,  that  no  under- 
taker or  other  person  shall  inter,  or  remove  from  the  town, 
the  body  of  a  deceased  person  without  a  permit  from  the 
board  of  health ;  that  such  permit  shall  not  be  issued  until  a 
physician  has  filed  a  certificate  with  the  board  of  health  giving 
the  name,  sex,  age,  color,  nature  of  illness,  and  cause  of 


16 


SANITARY    SCIENCE. 


I. 


death  of  that  person.  In  this  manner  every  death  in  every 
town  immediately  goes  on  record,  and  the  local  boards  of 
health  transmit  these  records  monthly  to  the  state  authorities. 
The  attempt  to  collect  this  information  annually  through 
assessors,  as  has  been  done  in  Pennsylvania,  results  in  entire 
failure  and  in  the  waste  of  public  money.  The  method 
above  described  is  simple  and  effectively  collects  the  desired 
facts.  Moreover,  as  the  physicians'  certificates  are  daily 
placed  on  file,  the  board  of  health  has  constant  information  as 
to  the  degree  of  prevalence  of  each  disease  in  the  town  and 
is  able  to  take  proper  measures  to  prevent  the  spread  of 
infection. 

The  total  number  of  deaths  from  all  causes  in  the  registra- 
tion area  of  the  United  States  and  the  rate  of  mortality  for 
each  1000  inhabitants  is  shown  in  the  following  table : 

DEATHS  IN  UNITED  STATES  REGISTRATION  AREA 


Year. 

Total  Deaths. 

Rate  per  1000. 

Year. 

Total  Deaths. 

Rate  per  1000. 

1880 

178645 

19.8 

1911 

839  284 

14.2 

1890 

386  212 

19.6 

1912 

838  251 

13-9 

1900 

539  939 

I7.6 

1913 

890  848 

14.1 

IQOS 

545  533 

16.0 

1914 

898  059 

13.6 

1910 

805412 

15-0 

1915 

909  155 

13-5 

The  yearly  death  rate  is  greater  in  the  cities  than  in  the 
country.  In  1900  the  highest  death  rate  for  any  city  in  the 
United  States  was  39.7  for  Natchez,  Miss.,  while  the  lowest 
was  9. 1  for  St.  Joseph,  Mo.  The  mortality  of  the  colored 
population  is  materially  greater  than  that  of  the  white  popu- 
lation;  for  instance,  in  1900  New  York  had  a  death  rate  of 
20.3  per  thousand  for  the  white  and  29.3  for  the  colored 
population.  Chicago  had  16. 1  for  white  and  21.6  for  colored, 
and  Charleston,  S.  C.,  had  25.6  for  white  and  46.7  for 
colored. 


STATISTICS   OF   MORTALITY. 


1 60 


In  1912,  244.1  of  every  1000  deaths  were  of  children  under 
the  age  of  five  years.  The  least  number  of  deaths  occurred 
among  children  between  the  ages  of  10  to  14  years,  inclusive, 
there  being,  for  this  age,  but  13.6  deaths  out  of  every  1000. 
The  medium  age  of  the  people  of  the  United  States  was,  in 
1910,  about  24.5  years;  that  is,  one-half  of  the  population  is 
younger  and  the  other  half  older  than  24.5  years.  It  is 
therefore  clear  that  the  work  of  sanitary  scientists  and  of 
boards  of  health  should  be  especially  directed  to  the  improve- 
ment of  the  conditions  that  surround  the  young,  in  order  that 
the  median  age  of  the  population  may  be  raised.  If  physicians 
were  paid  to  watch  over  children  when  well,  no  doubt  better 
results  would  be  secured  than  under  the  present  plan  of  rely- 
ing upon  cure  by  drugs  rather  than  upon  prevention  by  hygiene. 
Nowhere  does  the  old  adage,  "  an  ounce  of  prevention  is  worth 
a  pound  of  cure,"  better  apply  than  in  the  case  of  sickness 
among  the  young. 

The  following  table  shows  the  death  rate  per  1000  inhabitants 
for  the  principal  countries  of  the  world  in  which  such  records 
are  kept.  Those  for  the  United  States  are  for  the  registration 
area  only  and  are  for  those  States  in  which  the  laws  for  the 
registration  of  deaths  are  of  such  character  and  so  enforced  by 
the  State  authorities  as  to  warrant  the  inclusion  of  the  returns 
in  the  census  reports  on  mortality  statistics. 

DEATH  RATES  PER  1000  INHABITANTS. 


1900 

1905 

1910 

I9IS 

United  States  

17.6 

16  o 

iq    o 

it  6 

England  and  Wales  .  .  . 

18  2 

it  -2 

15    tr 

14.   O 

Germany 

22    I 

IQ    8 

16  2 

France             .  .  . 

21    O 

io  6 

17    8 

io  6 

Italy 

23    8 

22    O 

10   O 

17    I 

Spain  

28.0 

25.8 

23    3 

22    I 

Chile 

75  6 

•24    Q 

•21    o 

27  8 

1 6b 


SANITARY   SCIENCE, 


I. 


The  lack  of  application  of  sanitary  principles  is  strikingly 
shown  in  the  death  rates  for  Chile,  which  are  double  those  for 
the  United  States  and  England.  This  same  condition  exists 
to  a  greater  or  less  extent  in  most  tropical  countries,  these 
being  among  the  last  to  apply  the  principles  of  sanitation,  but 
it  is  gratifying  to  note  that  these  countries  are  taking  up  the 
work  of  sanitation  and,  with  stable  governments  to  assist  in  the 
work,  the  southern  republics  should,  before  long,  be  as  health- 
ful places  as  the  countries  in  the  north  temperate  zones.  The 
results  obtained  in  the  Canal  Zone  at  Panama  since  1900 
show  what  is  possible  to  be  done  in  other  tropical  countries. 

The  following  table  shows  the  number  of  deaths  in  the 
registration  area,  reported  in  the  census  volume  of  mortality 
statistics  for  1915,  for  the  principal  zymotic  diseases. 

DEATHS  IN  THE  UNITED  STATES  IN  1915. 
(Registration  area  only). 


Cause  of  Death. 

Number  of 
Deaths. 

Percentage  of 
Deaths. 

Deaths  per 
1000  Living. 

From  all  causes                      .      ... 

QOO  IZ< 

IOO   O 

13  ^02 

Tuberculosis  (all  form). 

8l  QH 

0    ^ 

I    277 

Pneumonia  

55  825 

6.1 

o  820 

Diarrheal  diseases 

4O  OQQ 

4  4 

O    SOS 

Influenza  

10  768 

I.  2 

O.  1  60 

Diphtheria  and  Croup.               .... 

10  544 

I  .  2 

O    IS7 

Typhoid  fever 

8032 

O   O 

O    124 

Whooping  cough  

5  421 

0.6 

O.oSl 

Measles                                     .... 

3  649 

0.4 

o  oS4 

Scarlet  fever 

2  410 

o.  3 

o  036 

Malaria  

i  541 

O.  2 

0.023 

Smallpox                            

169 

0.003 

The  percentages  of  the  total  deaths  for  the  several  zymotic 
diseases  vary  greatly  in  different  parts  of  the  country;  in  the 
northern  States  diphtheria  and  typhoid  fever  are  more  prevalent 
than  in  the  southern  States,  while  the  reverse  is  the  case  for 
malarial  fever.  Tuberculosis  is  more  prevalent  in  the  cities 


STATISTICS    OF   MORTALITY. 


than  in  the  country;  thus,  in  New  Jersey  the  death  rate  in 
1900  was  2. 02  for  cities  and  1.51  for  rural  districts. 

The  decrease  in  the  death  rate  due  to  the  principal  zymotic 
diseases  is  well  shown  in  the  following  table.  The  decrease  in 
mortality  from  typhoid  fever  during  the  years  from  1900  to 
1915  is  of  particular  interest  to  the  sanitary  engineer,  as  his 
work  has  probably  been  more  closely  connected  with  its  eradi- 
cation than  that  of  any  other  disease.  Although  not  as  yet 
considered  a  zymotic  disease,  the  death  rates  for  cancer  are 
included  in  the  table.  The  cause  and  prevention  of  this  baffling 
disease  have  not  yet  been  discovered,  but  when  they  are  found 
the  work  of  sanitary  science  will  be  extended  to  include  this 
disease  with,  no  doubt,  a  lowering  of  its  death  rate. 

UNITED  STATES  DEATH  RATES  PER  100000  INHABITANTS. 


Cause. 

1900 

1905 

1910 

I9IS 

Tuberculosis  (all  forms) 

2OI    O 

IO2    3 

1  60   3 

i/itj   8 

Pneumonia  

180  <? 

148  8 

14.7   7 

1  32    7 

Diarrheal  diseases 

108  8 

O7    O 

100  8 

Diphtheria  and  croup  

A-2     1 

23    6 

21    A 

OV  •  O 

T  r    7 

Typhoid  fever.           

?e  Q 

27    8 

23    "? 

X0  •  / 
12    4 

12.  1 

10.6 

114 

8  i 

IVIeasles                         

12    <? 

7   % 

12    3 

<?   4 

IO.  2 

6.7 

II    6 

3    6 

Cancer                       

63  o 

71   4 

76    2 

81  i 

The  results  just  given  show  that  about  one-fourth  of  all 
deaths  in  the  United  States  result  from  causes  of  a  zymotic  or 
infectious  character.  Sanitary  science  seeks  to  decrease  this 
percentage  and  ultimately  to  render  these  diseases  as  infrequent 
as  smallpox  now  is.  By  so  doing  an  annual  death  rate  of  14 
per  thousand  will  be  lowered  to  10  per  thousand,  and  the  con- 
sequence will  be  a  marked  increase  in  the  average  age  of  the 
population.  Death  cannot  be  avoided,  but  it  is  the  duty  of 


1 8  SANITARY    SCIENCE.  I. 

man  to  prolong  his  life  to  the  highest  possible  limit  and  to 
render  it  free  from  preventable  disease. 

What  hygiene  and  sanitary  science  have  done  in  the  last 
two  hundred  years  may  be  appreciated  from  the  statement 
made  by  Farr,  about  1870,  that  the  annual  death  rate  of  the 
population  of  London  in  the  latter  half  of  the  seventeenth 
century  was  nearly  80  per  thousand,  in  the  eighteenth  century 
about  50  per  thousand,  and  soon  after  the  middle  of  the 
nineteenth  century  about  24  per  thousand.  To  this  may  be 
added  that  for  the  decade  1871-1880  the  average  yearly  death 
rate  of  London  was  22.7,  and  for  the  decade  1881-1890  it 
was  20.5  per  thousand  inhabitants. 

The  ancient  idea  that  contagious  and  infectious  diseases 
were  specially  inflicted  by  a  divine  providence,  as  a  punish- 
ment for  the  sins  of  people,  has  long  ago  been  discarded. 
Likewise  the  idea  maintaine.d  by  some  classic  writers  that 
such  diseases  arose  from  poisons  generated  by  decaying 
animal  matter  has  also  disappeared.  Not  until  after  the 
middle  of  the  nineteenth  century,  however,  did  it  become  proved 
that  such  diseases  are  caused  by  minute  germs,  called  bacteria, 
which  are  transferred  from  one  person  to  another  by  contact  or 
through  the  air.  This  having  been  established,  hygiene  and 
sanitary  science  were  placed  upon  a  firm  foundation. 

5.    BACTERIOLOGY.  , 

Most  of  the  germs  which  cause  zymotic  diseases  are  called 
Bacteria.  These  are  of  a  fungoid  nature,  and  belong  to  the 
lowest  class  in  the  vegetable  kingdom.  They  are  without 
color,  very  minute  in  size,  and  each  individual  consists  of  a 
single  cell  of  organic  matter  within  which  watery  fluid  is  con- 
tained. An  individual  bacterium  is  usually  about  one  one- 
thousandth  of  a  millimeter  in  diameter  or  thickness,  and 
hence  can  be  studied  only  under  high  microscopic  power. 
The  cells  are  spherical  or  cylindrical,  the  latter  form  being 
the  more  common;  the  word  bacterium,  meaning  a  little  rod, 


5.  BACTERIOLOGY.  19 

is  due  to  this  shape.  Propagation  generally  occurs  by  a  con- 
traction near  the  middle  of  a  cell  which  then  divides  into  two 
independent  cells.  When  the  conditions  of  temperature  and 
food  are  favorable  propagation  goes  on  with  great  rapidity, 
and  a  few  hours  may  be  sufficient  for  one  or  two  individuals 
to  multiply  into  millions. 

Bacteria  are  divided  into  three  families,  and  each  family  into 
several  genera,  the  family  division  being  according  to  form. 
Thus  the  Micrococci  are  generally  spherical  and  a  group  of 
these  somewhat  resembles  a  bunch  of  grapes;  the  Bacilli  are 
the  straight  cylindrical  rod-like  cells;  and  the  Spirilla  are  of 
curved  or  spiral  form.  The  genera  and  species  are  distin- 
guished partly  by  form  and  the  method  of  propagation,  but 
more  definitely  by  the  functions  that  they  perform  in  the 
economy  of  nature  or  by  the  diseases  with  which  they  are 
connected. 

The  functions  of  bacteria  are  always  connected  with  changes 
in  organic  matter,  and  these  changes  may  be  useful  or 
injurious.  The  useful  changes  are  those  of  fermentation  and 
the  alteration  of  decaying  organic  matter  into  harmless  con- 
stituents. The  injurious  changes  are  those  of  disease  by 
which  healthy  living  organisms  or  tissues  are  brought  into  a 
state  of  disorder  or  specific  poisoning.  Hence  bacteria  are 
divided  into  two  kinds  according  to  their  functions,  the  first 
being  the  useful  or  necessary  class  and  the  second  the  injurious 
or  parasitic  class.  % 

The  useful  bacteria  exist  in  the  soil,  the  air,  the  water,  and 
in  the  secretions  and  digestive  systems  of  all  animals  and  men. 
The  change  of  milk  into  butter,  or  of  wine  into  vinegar,  is 
accomplished  by  their  action.  All  fermentation  results  from 
chemical  changes  which  are  due  to  the  development  and  life 
of  these  bacteria.  All  decay  of  organic  matter  and  its  change 
into  harmless  constituents  is  due  to  them.  Without  them  the 
digestion  and  assimilation  of  food  could  not  occur,  and  the 
highly  organized  life  of  man  could  not  be  possible.  This 


20  SANITARY   SCIENCE.  I. 

class  of  bacteria,  hence,  is  the  most  useful  and  important  form 
of  life,  even  though  it  be  the  lowest. 

The  parasitic  bacteria,  likewise,  are  found  everywhere, 
endeavoring  to  increase  and  multiply  by  preying  upon  living 
organic  matter.  When  the  conditions  become  favorable  their 
multiplication  goes  on  with  great  rapidity,  an  injurious  fer- 
mentation or  poisoning  results,  the  living  tissues  begin  to 
decay,  and  disease  results.  Each  species  of  parasitic  bacteria 
produces  its  own  specific  disease,  some  attacking  plants  and 
trees,  others  animals  and  men,  while  still  others  prey  upon 
man  alone.  Thus  Bacillus  amylovorus  produces  the  apple 
blight,  Bacillus  anthracis  causes  anthrax  fever  in  cattle, 
Bacillus  tuberculosis  causes  consumption  in  men  and  animals, 
Bacillus  diphtheriae  is  always  found  in  cases  of  diphtheria, 
Diplococcus  lanceolatus  in  pneumonia,  Bacillus  coma  in 
cholera,  and  Streptococcus  variolae  in  smallpox.  The  genus 
Bacillus  ranks  above  all  others  in  parasitic  work,  and  over  two 
hundred  different  species  have  been  recognized  and  described. 

Exactly  how  the  operations  of  bacteria  are  performed  and 
why  such  different  diseases  are  caused  has  not  been  ascer- 
tained. Most  bacteria  simply  float  in  the  surrounding  fluid, 
but  others  are  capable  of  slight  motion  by  means  of  hair-like 
appendages.  The  thin,  colorless  cells  are  capable  of  some 
pulsation,  and  it  is  by  the  secretion  of  fluid  through  the  walls 
of  these  cells  that  their  useful  or  injurious  work  is  done.  If 
by  any  means  this  process  is  interrupted,  as  has  been  done  in 
some  experiments  by  a  dose  of  chloroform  administered  to  a 
colony  of  bacteria,  the  processes  of  reproduction  and  secretion 
are  stopped  and  the  useful  or  injurious  changes  in  the  organic 
matter  are  completely  suspended.  It  is  known  that  the 
useful  bacteria  require  a  certain  degree  of  moisture  and  heat, 
and  that  the  presence  of  oxygen  is  necessary  for  their  work. 
It  is  also  known  that  sunlight  prevents  their  development 
and  that,  when  living  in  water,  they  are  entirely  destroyed  by 
boiling  for  half  an  hour. 


6.  ORGANIC   MATTER.  21 

Aerobic  bacteria  are  those  which  require  oxygen  for  the 
performance  of  their  functions,  and  under  this  class  come  most 
of  the  useful  bacteria.  Anaerobic  bacteria  are  those  which 
require  little  or  no  oxygen  in  order  to  perform  their  work,  and 
under  this  class  come  most  of  the  bacteria  which  produce 
putrefaction.  Some  species  of  bacteria  may  be  aerobic  or 
anaerobic  according  to  the  kind  of  material  in  which  they 
develop. 

6.  ORGANIC  MATTER. 

Organic  matter  may  be  either  vegetable  or  animal,  living 
or  dead.  What  constitutes  the  essence  of  life  in  the  plant  or 
animal  is  a  deep  mystery,  but  of  the  phenomena  of  life  much 
has  been  learned.  Living  organic  matter  is  that  which  is 
undergoing  systematic  change  by  the  absorption  of  dead 
organic  matter  as  food ;  at  first  each  individual  has  a  growth, 
and  after  this  ceases  disease  or  decay  begins;  in  due  time 
death  ensues,  and  the  dead  matter  is  resolved  into  other  forms 
and  is  absorbed  by  other  living  individuals.  From  the 
bacteriological  point  of  view  it  is  seen  that  the  useful  bacte- 
ria promote  length  of  life,  while  the  parasitic  ones  tend  to 
shorten  it. 

Organic  matter  consists  mainly  of  Carbon  (C),  Hydrogen 
(H),  Nitrogen  (N),  and  Oxygen  (O).  For  instance,  starch  is 
C6H10O&  and  cane-sugar  is  CiaHaaOn ;  albumen  of  the  blood  is 
C7,H112N18SOaa;  wheat  flour  contains  about  65  per  cent  of 
starch,  13  per  cent  of  albuminoids,  2  per  cent  of  nitrogen, 
together  with  cellulose,  water,  and  ash  phosphates.  The 
body  of  an  animal  is  similar  in  composition  to  its  food,  for 
the  body  has  grown  by  the  assimilation  of  that  food.  Carbon 
supplies  heat  to  the  body  and  also  forms  fat,  while  nitrog- 
enous foods  furnish  the  material  for  the  muscles.  In  all 
organic  tissue,  and  especially  in  the  bones  of  animals,  there  are 
also  found  certain  compounds  of  the  metals  potassium  (K), 


22  SANITARY  SCIENCE.  I. 

sodium  (Na),  and  calcium  (Ca),  such  as  sodium  chloride 
(NaCl),  or  common  salt,  and  potassium  nitrate  (KNO,),  or 
saltpeter. 

A  plant  absorbs  water  (H,O)  and  carbon  dioxide  (CO,)  from 
the  atmosphere  and  soil,  and  also  nitrates  of  the  metallic 
elements  from  the  soil.  A  nitrite,  it  will  be  remembered,  is 
the  result  of  the  combination  of  nitrous  acid  (HNO2)  with  a 
metallic  alkali,  while  a  nitrate  is  formed  by  the  stronger  nitric 
acid  (HNO3);  thus  potassium  hydroxide  (KOH),  or  potash, 
acted  on  by  nitrous  acid  yields  potassium  nitrite  (KNO,),  but 
when  acted  on  by  nitric  acid  it  yields  potassium  nitrate 
(KNO3).  From  this  food  the  plant  grows,  and  in  due  time  it 
becomes  either  food  for  animals  and  men  or  suffers  decay. 
In  the  animal  the  organic  matter  is  worked  over  into  new 
forms,  and  it  likewise  finally  becomes  either  food  or  decaying 
substance.  The  dead  and  decaying  matter  is  then  resolved 
back  into  carbon  dioxide,  water,  and  nitrates  in  the  manner 
now  to  be  described. 

The  following  diagram  represents  dead  organic  matter  as 
attacked  by  the  oxygen  (O)  of  the  atmosphere.  Here  M 
represents  potassium,  sodium,  and  the  other  metals  which  are 
found  as  compounds  in  the  dead  organic  matter.  If  the  tem- 


T^--HNO--HNO--MNO-- 
TRANSFORMATION  OF  DEAD  INTO  LIVING  ORGANIC  MATTER. 

perature  is  sufficiently  high  the  bacteria  begin  their  useful 
work,  and  the  first  result  is  that  the  oxygen  (O)  combines 
with  the  carbon  (C)  to  form  carbon  dioxide  (CO2).  Next  the 
oxygen  proceeds  to  attack  the  hydrogen  (H)  and  nitrogen  (N), 
and  ammonia  (NH8)  is  formed.  By  further  attacks  of  the 
surrounding  oxygen  there  are  formed  water  (H,O)  and  nitrous 


/.  FILTH   AND   DISEASE.  23 

acid  (HNO,),  which  finally  becomes  nitric  acid  (HNO,),  and 
the  action  of  this  on  the  metallic  compounds  in  the  soil  results 
in  the  nitrates  (MNO3).  Then  living  organic  matter  picks  up 
these  constituents  as  the  necessary  food  for  its  growth. 

The  most  remarkable  thing  about  this  process  of  decay  is 
that  it  requires  the  presence  and  active  work  of  bacteria.  In 
particular,  the  process  of  nitrification,  or  the  oxidation  of  the 
ammonia  to  nitrous  and  nitric  acid,  is  a  chemical  operation 
which  is  thought  to  be  impossible  without  the  operation  of 
certain  species  of  bacteria.  At  first  their  numbers  are  enor- 
mous, but  as  the  nitrous  acid  changes  to  nitric  they  become 
less  numerous,  and  when  the  nitrates  have  been  fully  formed 
few,  if  any,  bacteria  remain.  Thus  the  work  of  these  bacte- 
ria is  done  at  the  expense  of  their  life;  and  it  is  thought  that 
without  this  life  and  work  no  higher  forms  of  life  could  be 
possible. 

T.  FILTH  AND  DISEASE. 

In  Art.  2  it  was  shown  that  the  filthy  habits  and  unclean 
surroundings  of  the  people  of  the  middle  ages  resulted  in 
horrible  diseases  of  an  epidemic  nature.  The  reason  for  this 
may  now  be  understood.  Disease  is  caused  by  bacteria,  and 
wherever  filth  and  decay  abound  there  are  bacteria  in  count- 
less myriads.  It  is  true  that  the  bacteria  which  are  trans- 
forming decaying  matter  into  harmless  constituents  are  doing 
good  work,  but  it  is  also  true  that  under  conditions  of 
abundant  food  the  noxious  as  well  as  the  useful  bacteria  find 
opportunity  for  growth  and  multiplication.  Moreover,  in 
decaying  organic  matter  worms  and  insects  abound  upon 
which  parasitic  bacteria  are  preying.  Thus  filth  causes  the 
specific  bacteria  of  germ  diseases  to  increase  and  multiply,  the 
surrounding  atmosphere,  water,  and  soil  become  impregnated 
with  them,  and  then  they  make  their  attacks  upon  man. 
Further,  the  inhabitants  of  a  community  whose  streets, 


24  SANITARY   SCIENCE.  I. 

houses,  and  persons  are  unclean  usually  do  not  have  as 
nourishing  food,  systematic  exercise,  and  refreshing  sleep  as 
those  who  live  under  good  hygienic  conditions.  Consequently, 
their  general  power  of  resistance  to  disease  is  of  a  low  order, 
and  when  an  epidemic  comes  they  readily  fall  before  it.  Each 
epidemic  causes  greater  and  greater  debilitation,  the  diseases 
increase  in  virulence,  and  finally  the  horrible  black  death 
sweeps  over  the  land.  Forty-five  epidemics  of  this  plague 
occurred  in  Europe  during  the  seventeenth  century,  and  in 
the  year  1665  it  caused  about  65  ooo  deaths  in  the  city  of 
London,  which  then  had  a  population  of  only  200  ooo. 

It  is  not  at  all  necessary  to  accept  the  above  reasoning  in 
order  to  establish  the  connection  between  filth  and  disease, 
for  this  is  done  most  effectively  by  facts.  All  statistics  show 
that  the  rate  of  mortality  is  greater  in  the  city  than  in  the 
country,  and  that  the  highest  mortality  in  a  city  is  found  in 
the  tenement  districts,  where  streets,  houses,  and  people  are 
unclean.  Again,  by  the  introduction  of  a  pure  water  supply 
and  the  construction  of  a  sewerage  system  it  is  found  that 
the  mortality  from  dangerous  zymotic  diseases  is  markedly 
decreased.  Thus,  at  Manila,  in  the  Philippine  Islands, 
cholera  was  endemic  prior  to  1890,  and  frequently  there  were  a 
hundred  deaths  in  a  single  day,  but  since  the  introduction  of 
a  water-supply  system  it  has  almost  disappeared.  Again,  at 
Danzig,  in  Germany,  the  annual  death  rate  from  typhoid  fever 
during  1865-69  was  i.i  per  thousand  inhabitants;  during 
1871-75,  after  the  introduction  of  water  supply,  it  was  0.9; 
and  during  1876-80,  after  the  completion  of  a  sewerage 
system,  it  fell  to  0.2  per  thousand.  Similar  examples  in  great 
number  might  easily  be  given  to  illustrate  how  the  removal 
of  filth  causes  disease  to  decrease. 

The  solid  excrement  of  man  is  a  dangerous  form  of  filth,  and 
particularly  that  from  a  person  ill  with  fever.  Three  or  four 
hundred  years  ago  the  usual  method  of  its  disposal  in  the 
cities  of  Europe  was  to  throw  it  into  the  streets  and  trust  to 


8.  IMPURE  AIR  AND   DISEASE.  2$ 

the  rainfall  to  wash  it  away.  Clothing  infected  with  the  dis- 
charges of  sick  persons  was  washed  near  public  fountains  or 
in  streams  from  which  drinking  water  was  obtained,  and  as  a 
consequence  disease  was  spread  in  all  directions.  Such  prac- 
tices are  now  forbidden  by  law  in  Europe,  but  they  continue 
in  many  countries.  In  India  it  is  still  customary  to  throw 
human  excreta  upon  the  surface  of  the  ground  and  to  drink 
water  in  which  people  have  just  bathed;  as  a  consequence, 
cholera  is  always  present  and  at  times  rages  with  great  viru- 
lence. Yet  there  are  localities  in  India  where  the  people  have 
adopted  the  European  modes  of  living,  and  these  are  almost 
wholly  free  from  cholera. 

The  experience  and  the  statistics  of  the  past  two  centuries 
teach  most  forcibly  that  the  prevention  of  zymotic  diseases 
in  a  town  is  to  be  effected  in  five  principal  ways:  first,  by 
proper  hygiene  of  individuals  as  regards  exercise,  food,  and 
cleanliness;  second,  by  vaccination  against  smallpox  and  by 
disinfection  and  quarantine  of  persons  having  dangerous  con- 
tagious diseases;  third,  by  proper  heating  and  ventilation  of 
the  houses;  fourth,  by  the  maintenance  of  a  pure  water  sup- 
ply; and  fifth,  by  the  removal  of  all  filth  from  the  town  and 
its  disposal  in  such  manner  that  no  contamination  of  the  water 
supply  may  occur.  The  first  and  second  of  these  methods 
are  to  be  carried  out  by  physicians  and  boards  of  health,  the 
third  is  the  province  of  the  architect,  the  fourth  and  fifth 
belong  to  sanitary  engineers.  Binding  all  together  are  the 
regulations  of  law,  which  empower  boards  of  health  to  sup- 
press nuisances,  punish  those  who  pollute  the  water  supply, 
and  require  the  cooperation  of  all  householders  in  disposing 
of  their  refuse  and  sewage. 

8.  IMPURE  AIR  AND  DISEASE. 

Many  zymotic  diseases  are  caused  by  infection  communi- 
cated through  the  air.  In  some  cases  insects  are  the  active 


26  SANITARY   SCIENCE.  1. 

agency;  for  instance,  Texas  fever  in  cattle  has  been  shown  to 
be  communicated  by  wood-ticks,  and  probably  the  infection 
of  malaria  is  propagated  by  the  help  of  mosquitoes.  Con- 
sumption is  caused  by  dust,  which  conveys  the  specific  bacteria 
of  that  disease  from  one  person  to  another;  the  dried  sputum 
of  a  consumptive  patient  has  been  shown  to  be  an  effective 
cause  of  such  infection,  and  hence  arose  the  recent  prohibi- 
tion by  boards  of  health  against  expectorating  on  the  floors 
of  public  conveyances  and  buildings.  Measles,  whooping- 
cough,  and  other  children's  diseases  may  probably  be  com- 
municated through  the  air  of  school-rooms,  and  perhaps  even 
from  house  to  house. 

Pure  air  consists  of  20.96  parts  of  oxygen,  79  per  cent  of 
nitrogen,  and  about  0.04  per  cent  of  carbon  dioxide.  It  is  a 
mechanical  mixture  and  not  a  chemical  compound,  and  hence 
the  percentages  just  given  are  liable  to  some  variation.  The 
proportion  of  oxygen  may  rise  almost  to  2  I  per  cent  on  the 
sea  or  on  high  mountains,  and  it  falls  to  20.8  or  20.7  in 
crowded  theatres  and  narrow  alleys.  The  depressing  effect 
of  low  oxygen  and  high  carbon  dioxide  in  an  ill-ventilated 
lecture  hall  are  known  to  all,  and  in  such  cases  the  animal 
matter  of  respiration,  floating  in  the  form  of  moisture  or  dust, 
is  particularly  liable  to  convey  the  germs  of  disease  from  the 
lungs  of  one  person  to  those  of  many  others. 

The  dust  that  floats  in  the  air  of  a  city  street  is  composed 
of  fine  grains  of  sand,  carbon,  or  smoke,  animal  manure  of  the 
streets,  decaying  vegetable  matter,  and  many  kinds  of  fungoid 
or  bacterial  growths.  When  it  is  considered  that  all  these 
impurities  are  brought  into  contact  with  the  blood  in  the  lungs 
it  is  not  strange  that  the  infectious  diseases  are  so  readily 
spread  by  means  of  the  air.  It  is  a  fact,  however,  that  the 
liability  to  such  infection  is  far  less  in  the  street  than  in  the 
house,  and  this  is  doubtless  due  to  the  circumstance  that  the 
street  air  is  in  continual  motion,  and  hence  the  dust  is  con- 
tinually supplied  with  fresh  oxygen  to  hasten  the  process  of 


8.  IMPURE   AIR   AND   DISEASE.  2/ 

decay  and  thus  reduce  the  number  of  bacteria  and  decrease 
their  virulence.  Within  doors  there  is  much  less  motion  of 
the  air,  fresh  supplies  of  oxygen  are  not  furnished  to  the 
decaying  dust,  carbon  dioxide  and  other  products  of  respira- 
tion and  transpiration  are  more  abundant,  and  consequently 
the  bacteria  become  more  numerous  and  virulent. 

It  is  hence  important  that  the  air  of  the  streets  should  be 
pure,  but  still  more  important  that  the  air  within  the  houses 
should  be  kept  so.  To  render  the  street  air  pure  the  street 
pavements  should  be  maintained  in  proper  cleanliness  by  fre- 
quent sweeping  or  washing,  and  by  the  removal  of  all  garbage 
and  decaying  matter  from  around  the  houses.  The  width  of 
streets  should  be  such  that  the  air  may  properly  circulate  and 
abundant  sunlight  enter.  The  stagnant  air  of  narrow  alleys 
and  damp  courts,  where  crowded  tenements  with  damp  cellars 
are  found,  is  a  most  efficient  propagator  of  disease,  and  in 
these  localities  the  highest  rate  of  mortality  is  found. 

When  the  air  of  the  streets  is  reasonably  pure  that  of  the 
houses  will  be  so  also,  if  the  weather  permits  the  windows  to 
be  open,  and  if  the  houses  and  their  inhabitants  be  cleanly. 
But  when  artificial  heat  is  required  in  the  houses  the  problem 
of  securing  efficient  ventilation  is  not  so  easy.  The  subjects 
of  heating  and  ventilation  must  indeed  be  treated  together  in 
order  to  satisfactorily  solve  the  problem.  This  is  the  province 
of  the  architect  rather  than  of  the  engineer,  and  numerous 
excellent  treatises  discuss  the  question  in  great  detail. 
Although  the  ventilation  of  houses  is  one  of  the  branches  of 
sanitary  science,  it  is  not  strictly  one  of  the  departments  of 
sanitary  engineering,  for  the  engineer's  work  is  the  execution 
of  improvements  for  the  general  public  rather  than  for  the 
private  individual.  The  architect  erects  the  house  and  pro- 
vides for  its  heating  and  ventilation,  the  engineer  keeps  the 
streets  clean,  builds  the  water-works,  and  provides  for  the 
removal  of  sewage.  By  the  work  of  both  professions  the  air 
within  and  without  the  house  is  to  be  kept  as  nearly  pure  as 


28  SANITARY   SCIENCE.  I. 

possible,  and  thus  both  the  health  of  the  family  and  of  the 
public  is  to  be  conserved. 

9.  DRINKING  WATER  AND  DISEASE. 

The  water  that  we  drink  is  assimilated  into  the  blood  in  the 
same  manner  as  food,  and  if  it  contain  the  bacteria  of  zymotic 
disease  infection  may  be  caused.  After  a  period  of  incuba- 
tion an  inflammation  of  the  intestines  generally  occurs,  fol- 
lowed by  fever  and  the  other  symptoms  of  the  disease. 
Persons  with  weak  constitutions  who  live  in  unclean  surround- 
ings are  most  liable  to  be  attacked,  while  the  strong  and  those 
who  observe  hygienic  laws  have  the  best  chances  of  escape. 

Cholera  and  typhoid  fever  are  generally  propagated  through 
drinking  water  which  has  been  infected  with  the  characteristic 
bacteria  of  these  diseases,  although  they  may  also  be  com- 
municated by  contagion  with  the  clothing  or  person  of  a  sick 
patient.  Diarrheal  and  other  intestinal  complaints  likewise 
result  from  the  use  of  impure  water.  Two  particular  instances 
will  now  be  given  to  illustrate  the  effects  that  follow  the 
infection  of  a  water  supply. 

In  1885  a  severe  epidemic  of  typhoid  fever  afflicted  the 
borough  of  Plymouth,  Pa.,  whose  population  was  then  about 
7800.  It  first  appeared  on  April  9,  and  there  were  713  cases 
during  April,  261  in  May,  and  later  130  cases,  making.in  all 
1104  cases  of  sickness.  The  number  of  deaths  was  114  or 
about  14^  for  each  thousand  inhabitants.  An  investigation 
clearly  showed  the  infection  to  have  been  caused  through  the 
water  supply  in  the  manner  that  will  be  explained  by  the  aid 
of  the  accompanying  plan.  A  is  the  reservoir  from  which  the 
town  was  generally  supplied  with  brook  water,  and  B,  C,  D 
are  collecting  reservoirs.  In  dry  seasons  this  supply  was 
insufficient,  and  in  very  cold  weather  it  also  failed  through 
freezing;  hence  in  such  cases  a  pump  P  furnished  river  water 
instead.  From  March  20  to  March  26  this  pump  supplied 


9.  DRINKING  WATER  AND   DISEASE.  29 

river  water  to  the  town,  and  then  the  pipes  at  A  were  thawed 
out,  the  pump  was  stopped,  and  the  brook  water  admitted  to 
the  mains.  At  H  is  a  house  where  from  January  to  March 
a  patient  lay  ill  with  typhoid  fever  contracted  probably  in 
December  at  Philadelphia.  The  excreta  of  this  patient  were 
thrown  out  upon  the  snow  near  the  edge  of  the  brook.  On 


PLAN  OF  WATER  SUPPLY  OF  PLYMOUTH,  PA. 

March  24  a  thaw  began  and  continued  rapidly  for  a  week  or 
more,  so  that  the  infection  doubtless  reached  the  town 
approximately  at  the  beginning  of  April.  As  the  period  of 
incubation  of  typhoid  is  twelve  or  fourteen  days,  this  brings 
us  to  April  10-15,  when  cases  were  rapidly  breaking  out  in 
Plymouth.  Thus  one  case  of  typhoid  multiplied  into  1104, 
produced  1 14  deaths,  and  caused  a  heavy  expense  to  the 
community,  the  amount  distributed  by  a  relief  committee 
being  $23  723,  while  the  total  loss  has  been  estimated  at 
$115  ooo. 

In  1892  a  terrible  cholera  epidemic  visited  the  city  of 
Hamburg,  in  Germany.  Adjacent  to  Hamburg,  and  forming 
with  it  one  continuous  city,  are  the  distinct  municipalities  of 
Altona  and  Wandsbeck.  Hamburg  used  the  unfiltered  water 
of  the  river  Elbe,  Altona  used  the  same  water  but  thoroughly 
filtered  it  through  sand  beds  before  delivery  into  the  pipes, 


30  SANITARY   SCIENCE.  I. 

while  Wandsbeck  derived  its  supply  from  a  lake.  On  August 
16  cholera  broke  out  and  7427  cases  occurred  in  August,  9341 
in  September,  and  181  in  October.  The  total  number  of 
deaths  was  8976,  the  deaths  in  Hamburg  being  134  per 
thousand  inhabitants,  in  Altona  23,  and  in  Wandsbeck  22. 
In  Hamburg  the  disease  prevailed  in  epidemic  form,  but  the 
boundaries  between  it  and  Altona  and  Wandsbeck  formed  the 
lines  beyond  which  the  epidemic  as  such  did  not  extend.  In 
one  street  which  for  a  long  distance  formed  part  of  the 
boundary  there  was  cholera  on  the  Hamburg  side,  whereas 
the  other  side  was  free  from  it.  Investigation  showed  that 
the  cholera  bacillus  was  found  in  the  water  of  the  Elbe,  and 
there  can  be  no  doubt  but  that  the  people  of  Hamburg  were 
infected  by  this  water,  while  the  filtration  of  the  Altona  sup- 
ply rendered  it  harmless. 

It  would  be  very  easy  to  fill  many  volumes  with  instances 
showing  how  epidemics  of  typhoid  fever  and  cholera  have  been 
produced  by  impure  water,  and  how  the  introduction  of  pure 
water  has  diminished  the  mortality  from  these  diseases.  The 
reports  of  sanitary  commissions  and  boards  of  health  abound 
in  such  illustrations,  and  the  statement  made  at  the  beginning 
of  this  article  is  as  thoroughly  established  as  the  fact  that 
smallpox  is  prevented  by  vaccination.  The  water  used  by  a 
town,  therefore,  must  be  maintained  pure  in  quality  in  order 
to  prevent  typhoid  and  other  allied  zymotic  diseases,  and  from 
time  to  time  it  should  be  examined  by  chemical  and  biological 
methods,  in  order  to  ascertain  whether  changes  are  occurring 
that  may  prove  threatening  or  injurious. 

10.  MATTER  IN  NATURAL  WATERS. 

Water  as  found  in  nature  always  contains  some  inorganic 
and  organic  matter.  Both  of  these  occur  in  two  forms,  in 
suspension  or  in  solution.  Suspended  matter  is  that  which  is 
floating  in  the  water,  like  inorganic  sand  or  silt ;  dead  organic 


10.  MATTER   IN   NATURAL   WATERS.  3! 

matter,  like  leaves,  sticks,  feathers,  and  animal  tissue;  or  live 
organic  matter,  like  desmids,  algae,  and  insects.  Suspended 
matter  may  be  in  large  part  removed  from  water  by  allowing 
it  to  settle  in  reservoirs  or  by  passing  it  through  filtering 
screens.  Dissolved  matter,  on  the  other  hand,  is  that  which 
is  so  thoroughly  in  solution  that  it  cannot  be  removed  by 
settling  or  by  screening,  and  the  nature  and  amount  of  this 
gives  to  different  drinking  waters  different  distinctive  charac- 
teristics. In  a  river  the  suspended  matter  during  periods  of 
high  water  may  be  ten  or  twenty  times  as  great  as  at  low 
water,  while  the  dissolved  matter  is.  rarely  twice  as  great;  in 
spring  water  the  variations  are  quite  small. 

It  is  clear  that  much  suspended  matter,  whether  inorganic 
or  organic,  renders  water  undesirable  and  perhaps  unfit  for 
domestic  use.  Silt  in  suspension  acts  unfavorably  upon  the 
intestines,  while  organic  matter  in  suspension  is  generally  in 
the  process  of  decay  and  hence  may  cause  zymotic  disease. 
A  water  which  is  turbid  in  appearance  generally  contains 
much  suspended  matter  and  this  should  be  removed  by 
settling  or  filtration  before  it  is  suited  for  a  public  supply. 
The  methods  for  doing  this  will  be  described  in  the  next 
chapter. 

All  natural  waters  contain  in  solution  certain  gases,  such  as 
oxygen,  nitrogen,  and  carbon  dioxide;  these  are  not  at  all 
injurious  to  health,  but  are  often  beneficial.  The  presence  of 
little  oxygen  is  generally  an  indication  of  impurity,  for  if  the 
water  contains  decaying  organic  matter  the  dissolved  oxygen 
is  used  for  its  combustion  and  nitrification.  The  agitation  of 
water,  in  order  to  introduce  oxygen  into  it,  is  in  fact  one  of 
the  'methods  of  purification  that  will  be  described  later. 
Dissolved  nitrogen  is  of  little  influence.  Dissolved  carbon 
dioxide  is  usually  beneficial  in  increasing  palatability,  but  if 
the  water  flows  through  a  limestone  country  this  gas  causes 
the  formation  of  carbonates  and  an  increase  in  the  hardness  of 
the  water. 


32  SANITARY  SCIENCE.  1. 

A  water  is  said  to  be  "  hard  "  when  it  contains  in  solution 
the  carbonates  and  sulphates  of  calcium  or  magnesium.  The 
effect  of  these  is  to  improve  the  water  in  taste,  but  when  it 
is  used  for  washing  these  carbonates  and  sulphates  must  be 
decomposed  by  the  action  of  soap  before  a  lather  can  be 
formed.  Hard  waters,  hence,  are  more  expensive  in  domestic 
use  than  soft  ones.  Hardness  is  said  to  be  "temporary" 
when  it  can  be  removed  by  boiling,  and  this  is  the  case  when 
carbonates  alone  are  present;  it  is  said  to  be  "  permanent  " 
when  boiling  is  not  sufficient,  but  soap  or  other  chemical 
means  are  required,  and  this  is  the  case  when  sulphates  are 
present.  Many  waters  contain  both  carbonates  and  sulphates, 
and  for  these  the  term  "total  hardness"  expresses  their 
combined  influence. 

Sodium  chloride,  or  common  salt,  is  found  in  all  natural 
waters,  the  proportion  being  much  higher  near  the  sea  coast 
or  in  the  vicinity  of  salt  beds  than  in  inland  surface  and  ground 
waters.  This  is  not  at  all  injurious  to  health,  but  if  the  pro- 
portion is  found  to  increase  in  a  well  or  water  supply  it  is  an 
indication  of  sewage  contamination,  for  sewage  contains  some 
of  the  salt  which  is  eaten  by  men  and  animals.  In  chemical 
analyses  chlorine  is  determined  instead  of  the  sodium  chloride, 
the  amount  of  the  former  being  always  proportional  to  that 
of  the  latter. 

Ammonia  in  water  indicates  the  presence  of  organic  matter 
in  an  advanced  stage  of  decay,  as  shown  by  the  diagram  in 
Art.  6.  The  amount  of  this,  though  very  small  and  not 
injurious  to  health,  is  a  valuable  indication  of  what  is  going 
on  in  the  water.  It  is  determined  in  two  forms,  called  "  free 
ammonia"  and .  "  albuminoid  ammonia."  Free  ammonia  is 
that  which  has  been  actually  set  free  in  the  water  in  the 
process  of  decay,  while  albuminoid  ammonia  is  that  which  has 
not  been  set  free  but  is  liable  to  bcome  so  under  further  active 
attacks  of  oxygen.  The  sum  of  the  two  gives  an  indication 
of  the  total  amount  of  organic  matter  in  the  water,  but  free 


II.  CHEMICAL  ANALYSIS  OF  WATER.  33 

ammonia  usually  indicates  greater  danger  than  does  albumi- 
noid ammonia. 

Nitrates  are  the  final  result  of  the  nitrification  action,  and 
the  amount  of  these  gives  much  valuable  information. 
Nitrites  are  an  incomplete  result  of  the  same  process.  The 
examination  of  a  water  usually  determines  "  nitrogen  as 
nitrites"  and  "nitrogen  as  nitrates,"  and  the  larger  the 
amount  of  these  the  greater  the  amount  of  organic  matter 
previously  in  the  water.  If  the  ammonia  be  very  low  and 
the  nitrates  high  the  water  has  been  completely  purified;  if 
the  reverse  is  the  case  the  decaying  process  is  going  on  and 
the  water  is  dangerous.  Nitrites  indicate  danger,  for  complete 
purification  is  not  effected  until  the  nitrification  has  resulted 
in  the  formation  of  nitrates. 

Absolutely  pure  water  contains  no  bacteria,  and  the  greater 
the  number  of  bacteria  the  more  impure  it  is.  A  bacterio- 
logical examination  of  water  is  hence  most  desirable;  if  few  or 
no  bacteria  are  found  the  water  may  be  regarded  as  one  that 
cannot  cause  zymotic  disease.  The  presence  of  the  bacterium 
called  Bacillus  coli  communis,  which  is  abundant  in  the  intes- 
tines of  men  and  animals,  indicates  contamination  by  sewage, 
and  a  very  small  number  of  these  is  sufficient  to  condemn  a 
water  for  drinking  purposes. 

11.  CHEMICAL  ANALYSIS  OF  WATER. 

It  is  not  here  intended  to  give  a  description  of  methods  of 
chemical  analysis  which  will  enable  a  student  to  perform  them, 
but  merely  an  account  which  will  furnish  him  with  such  intelli- 
gent ideas  that  he  can  better  understand  and  interpret  the 
analyses.  Of  course,  the  first  thing  to  do  is  to  get  the  water, 
and  about  a  gallon  is  needed.  This  should  be  collected  in  a 
glass  vessel  with  a  glass  stopper,  and  it  is  essential  that  the 
jar  should  have  been  sterilized  in  order  to  remove  all  organic 
matter  and  destroy  all  bacteria  that  may  have  been  within  it. 


34  SANITARY   SCIENCE.  I. 

Water  should  be  analyzed  soon  after  having  been  collected, 
for  if  it  be  impure  the  processes  of  oxidation  and  nitrification 
may  to  a  certain  extent  render  it  purer  after  a  few  days.  It 
should  not  be  strained  or  filtered,  as  the  object  of  the  analysis 
is  to  determine  the  purity  of  the  sample  collected. 

As  the  quantities  to  be  obtained  by  analysis  are  very  small, 
they  are  expressed  in  parts  per  million,  and  always  by  weight. 
One  part  per  million  is  hence  the  same  as  one  milligram  in  a 
kilogram;  thus,  if  chlorine  be  given  as  6.4  parts  per  million, 
this  means  that  one  kilogram  of  water  contains  6.4  milligrams 
of  chlorine.  Some  chemists  unfortunately  express  the  results 
in  parts  per  100  ooo  instead  of  in  parts  per  million. 

Hardness. — This  is  expressed  by  the  number  of  parts  of 
calcium  carbonate  (CaCO8)  contained  in  one  million  parts  of 
the  water;  or  if  calcium  sulphate  (CaSO4)  is  present  it  is 
reduced  to  an  equivalent  amount  of  calcium  carbonate.  To 
determine  this,  one  milligram  of  calcium  carbonate  is  dissolved 
in  one  liter  of  distilled  water,  and  the  amount  of  a  standard 
soap  solution  which  will  form  a  permanent  lather  with  this 
water  is  determined.  Then  the  standard  soap  solution  is 
applied  to  the  water  under  analysts,  and  the  amount  of  it 
needed  to  form  the  same  lather  is  proportional  to  the  parts 
per  million  of  calcium  carbonate  which  this  water  contains. 
Rain  water  has  a  hardness  of  about  5,  river  waters  from  50  to 
100,  while  limestone  waters  have  200  or  more  parts  per  mill- 
ion. The  term  alkalinity  is  often  used  for  temporary  hardness. 

Total  Solids. — This  term  indicates  the  total  solid  matter, 
both  organic  and  inorganic,  in  one  million  parts  of  the  water. 
About  one  hundred  grams  of  water  are  placed  in  a  platinum 
dish  of  known  weight  and  the  whole  accurately  weighed. 
The  water  is  then  entirely  evaporated  by  boiling,  and  the  dish, 
after  cooling  to  the  original  temperature,  is  again  weighed; 
this  last  weight  minus  the  original  weight  of  the  dish  gives 
the  total  solids  in  the  water  used.  If  the  dish  be  heated  to 


II.  CHEMICAL  ANALYSIS   OF  WATER..  35 

redness  the  organic  matter  is  burned  out,  while  the  remaining 
ash  shows  the  inorganic  matter.  Rain  water  may  have  the 
total  solids  as  low  as  20,  while  ground  waters  may  run  up  to 
500  parts  per  million. 

Chlorine. — This  is  determined  by  the  fact  that,  if  a  solution 
of  sodium  chloride  be  colored  yellow  with  potassium  chromate 
and  silver  nitrate  be  added,  white  silver  chloride  will  be  pre- 
cipitated until  all  the  chlorine  is  used  up,  and  then  the  red 
color  of  silver  chromate  is  seen.  The  solution  of  silver  nitrate 
is  first  standardized,  and  then,  being  applied  to  the  water 
under  analysis,  the  amount  required  to  produce  red  color  is 
proportional  to  the  parts  per  million  of  chlorine  contained  in 
that  water.  Inland  brook  and  spring  waters  have  from  I  to  5 
parts  per  million  of  chlorine,  but  near  the  sea  coast  the  pro- 
portion may  be  several  times  as  great. 

Free  Ammonia. — This  is  also  determined  by  a  color  test,  a 
certain  solution  of  mercury  chloride,  called  Nessler's  solution, 
yielding  a  brownish  yellow  coloration  with  the  smallest  trace 
of  ammonia.  The  color  produced  by  the  water  under  analy- 
sis is  compared  with  those  produced  by  standard  ammonia 
solutions,  and  thus  the  parts  per  million  of  free  ammonia  in 
the  given  water  are  known.  Water  having  0.05  parts  per 
million  is  probably  very  pure;  if  above  o.  I  it  is  suspicious,  and 
perhaps  dangerous. 

Albuminoid  Ammonia. — This  is  determined  by  first  distill- 
ing off  all  the  free  ammonia  and  then  adding  an  alkaline  solu- 
tion of  potassium  permanganate  to  oxidize  the  nitrogenous 
organic  matter  remaining  in  the  water.  By  this  oxidation 
ammonia*  is  set  free,  and  this  is  measured  by  the  Nessler  solu- 
tion in  the  same  manner  as  before.  This  ammonia  is  called 
albuminoid  because  albumen  gives  off  ammonia  when  treated 
with  potassium  permanganate.  The  amount  of  albuminoid 
ammonia  in  good  water  is  also  very  small,  0.05  being  a  very 
low  figure  and  0.50  a  high  one. 


36  SANITARY   SCIENCE.  I. 

Nitrogen  as  Nitrates  and  Nitrites. — The  amounts  of  these 
are  also  ascertained  by  color  tests,  which  will  not  here  be 
described,  comparison  being  made  by  standard  solutions.  In 
order  to  give  full  information  the  amount  of  nitrogen  as 
nitrates  and  nitrogen  as  nitrites  should  be  reported  separately, 
the  former  showing  a  more  perfect  nitrification  than  the 
latter.  In  good  waters  the  amount  of  nitrogen  as  nitrates 
may  be  as  high  as  I  or  2  parts  per  million  while  that  of 
nitrogen  as  nitrites  is  a  mere  trace. 

Oxygen  Consumed. — This  term  means  the  amount  of 
oxygen  absorbed  by  the  water  from  potassium  permanganate, 
which  is  added  gradually  until  the  purple  color  remains  per- 
manent for  ten  minutes.  The  oxygen  set  free  from  the 
potassium  permanganate  is  absorbed  in  oxidizing  the  organic 
matter,  and  thus  the  greater  the  amount  consumed  the  more 
impure  is  the  water.  Less  than  one  part  per  million  indicates 
purity,  while  as  high  as  4  or  5  probably  indicates  danger. 

The  determination  of  hardness  is  needed  mainly  in  the 
examination  of  a  proposed  water  supply.  For  an  established 
supply  the  determinations  above  noted  are  those  generally 
made  in  order  to  judge  of  the  degree  of  purity,  and  the  cost 
of  such  an  analysis  should  be  less  than  $20.  Total  solids  are 
often  reported  in  two  parts;  the  one  indicating  organic  matter 
is  sometimes  called  **  loss  on  ignition/'  while  the  one  showing 
the  inorganic  matter  is  termed  "  fixed  residue.*'  Many 
analyses  omit  the  determination  of  oxygen  consumed. 

12.  BIOLOGICAL  ANALYSIS  OF  WATER. 

The  general  properties  of  a  water  as  regards  color,  odor, 
and  taste  are  usually  reported  both  in  chemical  and  biological 
work,  and  such  reports  are  of  value  as  indicating  suspicion 
only.  The  words  brown  or  yellow,  as  applied  to  color,  and 
vegetable,  fishy,  and  mould,  as  applied  to  color  and  taste, 
certainly  give  unpleasant  impressions.  It  goes  without  saying 


12.  BIOLOGICAL  ANALYSIS  OF  WATER.  37 

that  water  having  a  turbid  appearance  and  unpleasant  smell 
is  suspicious,  but  it  does  not  necessarily  follow  that  it  is 
dangerous.  A  statement  that  water  is  free  from  color  and 
odor  has,  however,  no  especial  significance,  for  some  noted 
epidemics  of  cholera  and  typhoid  fever  have  been  caused  by 
clear  and  sparkling  waters. 

A  microscopic  examination  is  valuable  in  ascertaining  the 
kinds  of  suspended  organic  matter  which  the  water  contains. 
The  dead  organic  matter  may  be  found  to  be  either  vegetable 
or  animal,  and  it  may  be  also  ascertained  what  particular 
plants  or  animals  furnish  the  refuse.  The  living  organic 
matter  will  in  general  be  found  to  be  certain  species  of  the 
fresh-water  algae  of  the  desmid  and  diatom  families. 

Desmids  are  of  greenish  color,  while  the  diatoms  are 
brownish  and  have  a  somewhat  silicious  structure.  Desmids 
have  not  given  trouble  in  water  supplies,  but  the  diatoms 
often  do  so,  as  when  they  decay  a  fishy  or  pig-pen  odor  is 
produced.  The  genera  Crenothrix  and  Volvox,  in  particular, 
often  cause  these  disagreeable  odors,  but  it  cannot  be  defi- 
nitely said  that  they  are  the  cause  of  disease.  These  families 
are  the  lowest  ones  in  the  vegetable  kingdom  which  have 
color,  the  still  lower  class  of  bacteria  being  colorless.  They 
can  easily  be  recognized  by  a  microscope  magnifying  about 
200  times,  while  the  bacteria  require  microscopes  of  the 
highest  power.  In  complete  biological  analyses  records  are 
made  of  the  number  of  each  genus  of  diatoms  and  other  algae 
contained  in  one  cubic  centimeter  of  the  water. 

The  bacteriological  examination  is,  however,  the  important 
part  of  a  biological  analysis.  The  object  of  this  is  to  deter- 
mine the  number  of  bacteria  present  in  one  cubic  centimeter 
of  the  water,  and  from  this  number  to  judge  of  its  purity. 
If  no  bacteria  are  found  it  is  inferred  that  the  water  cannot 
communicate  zymotic  disease,  and  the  larger  the  number 
found  the  greater  is  its  liability  to  do  so.  Good  water  con- 
tains less  than  100  bacteria  per  cubic  centimeter. 


38  SANITARY   SCIENCE.  I. 

In  order  to  count  the  bacteria,  a  culture  jelly,  consisting  of 
gelatine,  albumen,  and  extract  of  beef,  is  prepared  in  order 
to  furnish  food  upon  which  the  bacteria  may  feed  and  multi- 
ply. One  cubic  centimeter  of  water  is  then  thoroughly  mixed 
with  about  10  cubic  centimeters  of  liquefied  culture  jelly,  and 
the  whole  spread  out  in  a  thin  layer  upon  a  sterilized  dish  to 
harden.  Each  individual  bacterium  then  begins  to  eat,  to 
divide  by  fission,  and  the  multiplication  continues  until  a 
colony  is  produced  which  is  visible  to  the  eye.  After  about 
48  hours  the  number  of  colonies  is  counted,  and  thus  the 
number  of  bacteria  in  one  cubic  centimeter  of  the  water  is 
known.  When  the  number  is  large  a  plate  of  glass  ruled  into 
squares  is  used,  and  the  count  is  made  over  a  certain  frac- 
tional part  of  the  dish. 

By  further  examination  with  the  microscope  the  different 
species  of  bacteria,  may  be  ascertained,  but  this  is  rarely  done, 
as  it  requires  expert  skill  of  a  high  order.  In  fact,  the  entire 
bacteriological  analysis  requires  much  skill,  in  order  to  prevent 
the  introduction  of  bacteria  upon  the  gelatine  from  other 
sources  than  that  of  the  water  under  analysis. 

The  dangerous  bacilli  called  coli  communis,  or  coli  bacteria, 
are  detected  by  the  gas  which  they  produce  in  a  closed  tube. 
The  same  is  the  case  with  the  bacillus  of  typhoid  fever  and 
other  allied  forms.  One  cubic  centimeter  of  water  may  be 
tried,  as  also  ten  cubic  centimeters;  a  water  which  gives  a 
trace  of  gas  from  one  cubic  centimeter  is  considered  dangerous, 
while  one  which  gives  no  trace  from  ten  cubic  centimeters  is 
regarded  as  practically  free  from  this  contamination. 

A  popular  test  for  water,  known  as  Heisch's  sugar  test, 
and  which  may  easily  be  made  by  any  one,  will  here  be  noted, 
as  it  depends  entirely  upon  the  development  of  bacteria. 
Let  a  pint  bottle  of  colorless  glass,  and  having  a  glass  stopper, 
be  thoroughly  cleaned  by  immersion  in  boiling  water  for  half 
an  hour.  Let  it  be  entirely  filled  with  the  water  to  be 
examined,  and  let  a  teaspoonful  of  white  sugar  be  added. 


13.  INTERPRETATION   OF   ANALYSES.  39 

Then  let  it  be  exposed  to  the  light  in  the  window  of  a  warm 
room  for  a  week  or  ten  days.  If  the  water  becomes  turbid  it 
is  open  to  grave  suspicion,  but  if  it  remains  clear  it  is  almost 
certainly  safe. 

13.  INTERPRETATION  OF  ANALYSES. 

The  chemical  methods  of  analysis  have  been  longer  known 
and  are  better  systematized  than  the  biological  ones;  they 
are  found  recorded  and  interpreted  in  the  annals  of  sanitary 
science,  and  hence  on  the  whole  give  more  important  and 
extended  information  than  the  biological  analyses.  Un- 
doubtedly both  methods  of  analysis  will  go  hand  in  hand  in 
the  future,  the  biological  work  will  be  further  perfected,  and 
each  method  will  be  found  necessary  to  supplement  the  other. 

It  must  not  be  supposed  that  a  single  chemical  analysis  can 
give  decisive  information  as  to  whether  a  water  is  good  or 
dangerous.  In  certain  cases  it  may  do  so,  but  in  most  cases 
the  interpretation  of  the  results  cannot  be  made  unless  the 
source  from  which  the  water  was  taken  is  known.  This  is 
due  to  the  circumstance  that  the  substances  determined  in 
the  chemical  work  are  not  poisonous,  but  that  they  are  merely 
indicative  of  the  amount  of  organic  matter  in  the  water. 
Organic  matter  does  not  cause  disease  unless  in  such  a  state 
of  decay  that  bacteria  are  at  work,  and  whether  or  not  this  is 
the  case  depends  upon  the  physical  surroundings.  A  river 
water  high  in  albuminoid  ammonia  and  low  in  nitrates  may 
sometimes  be  less  injurious  than  a  spring  water  where  the 
former  is  low  and  the  latter  high.  Chlorine  gives  little  infor- 
mation unless  the  normal  chlorine  of  the  surrounding  region 
is  known.  In  short,  a  knowledge  of  the  topography  and  sani- 
tary conditions  of  the  source  of  supply  are  absolutely  essential 
in  order  to  interpret  satisfactorily  a  chemical  analysis.  After 
reading  the  next  chapter,  in  which  the  qualities  of  different 
kinds  of  waters  are  discussed,  the  truth  of  this  statement  will 
be  better  appreciated. 


40  SANITARY   SCIENCE.  I. 

There  is  a  widespread  idea  among  the  public  that  a  chemist 
should  not  know  the  origin  of  a  water,  in  order  that  he  may 
be  unbiased  in  giving  an  opinion.  Probably  this  arises  from 
the  impression  that  a  chemist  judges  of  the  influence  of  the 
ammonias  and  nitrates  in  the  same  manner  that  he  does 
regarding  such  poisons  as  arsenic  and  lead.  From  what  has 
been  said  in  this  and  the  preceding  articles,  it  is  seen  that  this 
is  not  at  all  the  case.  These  substances  are  not  poisons,  but 
merely  indications  of  the  amount  of  organic  matter  in  the 
water,  and  no  reliable  chemist  will  venture  to  give  an  opinion 
as  to  the  purity  of  water  without  knowing  its  source  and 
surroundings. 

In  the  case  of  water  infected  with  the  bacteria  of  cholera 
or  typhoid  fever  chemical  analysis  will  generally  fail  to  give 
any  indication  of  such  infection.  This  is  because  the  amount 
of  infected  matter  and  its  accompanying  bacteria  is  generally 
so  very  small  as  not  to  add  appreciably  to  the  amount  of 
organic  matter  previously  present.  In  an  experiment  by 
Latham  the  dejections  of  a  cholera  patient  were  added  to 
pure  water  in  sufficient  amount  to  impart  the  disease  to  any 
one  who  should  drink  it,  and  yet  chemical  analysis  entirely 
failed  to  discover  any  essential  difference  between  the  two 
waters.  In  such  a  case  a  single  bacteriological  analysis  may 
be  far  more  valuable  than  hundreds  of  chemical  ones,  and  in 
general  each  succeeding  year  adds  to  the  importance  of  such 
examinations. 

In  most  books  there  are  given  what  arc  called  "  standards 
of  purity,"  that  is,  certain  limits  beyond  which  a  water  is  to 
be  regarded  as  dangerous  in  use,  or  certain  figures  which  are 
regarded  as  reasonably  safe.  Such  standards  necessarily 
differ  in  different  localities  and  with  different  kinds  of  water, 
and  on  the  whole  can  be  regarded  only  as  expressions  of  indi- 
vidual opinion.  For  instance,  the  rules  of  the  Michigan  State 
Laboratory  of  Hygiene,  in  force  in  1897,  give  the  following 
parts  per  million  as  maximum  allowable  limits  for  drinking 


13.  INTERPRETATION  OF  ANALYSES.  «fl 

water:  Hardness,  50;  Total  Solids,  500,  of  which  the  inor- 
ganic should  not  exceed  200;  Chlorine,  12.1 ;  Free  Ammonia, 
0.05;  Albuminoid  Ammonia,  0.15;  Nitrogen  as  Nitrates, 
0.9;  Nitrogen  as  Nitrites,  a  trace;  Oxygen  consumed, 
2.2;  Bacteria,  '"  no  toxicogenic  germs,  as  demonstrated 
by  tests  on  animals."  These  standards  are  severe  ones,  and 
it  may  be  said  again  that  the  true  method  of  judging  the 
quality  of  a  water  is  not  by  observing  whether  one  of  the 
determinations  reaches  or  surpasses  a  certain  limit,  but  by 
studying  the  analysis  as  a  whole  in  the  light  of  the  source  and 
surroundings  of  the  water.  It  is  not  to  be  expected  that  the 
student  can  do  this  at  the  outset,  for  much  experience  and 
judgment  are  needed  in  order  to  announce  confident  conclu- 
sions. Indeed,  these  should  not  be  generally  announced 
without  a  study  of  several  analyses  of  the  water  taken  at 
different  times,  for  it  is  found  that  the  proportions  of  total 
solids,  ammonias,  and  nitrates  are  different  at  different  seasons 
of  the  year. 

The  following  figures  will  assist  the  student  to  form  an  idea 
of  the  difference  between  the  analyses  of  a  good  water  and  a 
very  impure  water,  like  sewage: 

Good  Water.  Sewage. 

Total  solids,           parts  per  million  50.0  700.0 

Organic  matter,                                30.0  200.0 

Inorganic  matter,       "                     20.0  500.0 

Chlorine,                                                  3.0  40.0 

Free  ammonia,                                        o.oio  25.000 

Albuminoid  ammonia,  "                       o.ioo  10.000 

Nitrogen  as  nitrates,      "            "          0.200  o.ioo 

Nitrogen  as  nitrites,      "                       o.ooo  0.005 

Oxygen  consumed,                                0.5  40.0 

Bacteria  in  one  cubic  centimeter        50  i  ooo  ooo 

Coli  bacteria,  in  10  cubic  cent.            o  5  ooo 

These  may  be  called  typical  analyses,  because  they  are  not 
actual  ones,  but  express  rough  average  figures  which  are 
intended  to  show  the  marked  differences  between  the  two 


42  SANITARY   SCIENCE.  I. 

types  of  water.  The  decimal  places  are  carried  out  in  each 
case  as  far  as  usual  in  analyses,  but  as  these  have  here  no 
significance  they  are  filled  with  ciphers.  Of  course,  different 
kinds  of  good  water  and  of  sewage  will  furnish  analyses  that 
may  differ  very  much  from  these  typical  ones. 

14.  RESULTS  OF  SANITARY  SCIENCE. 

In  the  preceding  pages  have  been  briefly  outlined  those 
elements  of  sanitary  science  which  are  essential  to  the  study 
of  sanitary  engineering.  The  historical  notes  show  what  was 
done  in  early  times  and  point  out  how  the  filthy  habits  of  the 
people  of  the  middle  ages  led  to  direful  epidemics  of  plague. 
The  classification  of  diseases,  the  statistics  of  mortality,  and 
the  section  on  bacteriology  explain  the  modern  theory  of  the 
transmission  of  zymotic  disease  by  means  of  organic  germs. 
The  changes  in  organic  matter  during  decay  are  next  discussed, 
and  it  is  seen  that  the  chemical  operations  require  the  pres- 
ence of  bacteria  to  secure  successful  purification.  Thus  the 
methods  by  which  filth  originates  disease  and  causes  its  com- 
munication to  men  through  air  and  water  are  rationally  under- 
stood. It  then  follows  that  streets  and  houses  should  be  well 
ventilated,  that  a  pure  supply  of  water  should  be  maintained, 
and  that  effective  drainage  and  sewerage  should  remove  all 
filth  from  the  town.  The  chemical  and  biological  methods  of 
analyzing  water  are  then  taken  up,  and  thus  the  foundation 
is  laid  for  the  discussions  of  the  qualities  of  water  and  the 
methods  of  its  purification  which  are  to  be  given  in  the  next 
chapter. 

Many  instances  have  been  given  showing  how  zymotic  dis- 
eases have  been  lessened  in  extent  and  intensity  by  the 
observance  of  the  principles  of  sanitary  science.  There  still 
remains,  however,  the  question  as  to  what  extent  the  average 
age  of  the  community  has  been  increased  by  the  great  reforms 
of  the  nineteenth  century.  In  order  to  answer  this  question 


RESULTS    OF    SANITARY    SCIENCE. 


43 


discussions  have  been  made  from  the  populations  found  in 
seven  censuses  of  the  United  States,  and  the  conclusions 
derived  will  now  be  presented.  Notwithstanding  the  many 
errors  and  imperfections  of  a  public  census,  owing  to  in- 
correct answers  given  by  the  people  and  to  carelessness  of 
the  enumerators,  these  errors  are  governed  by  definite  laws, 
which  are  the  same  in  all  the  censuses.  Accordingly,  the 
enumeration  of  the  people  by  ages  may  be  confidently  used 
to  furnish  results  from  which  accurate  comparisons  and  con- 
clusions can  be  drawn. 

The  following  table  gives  the  median  age  of  the  people  of 
the  United  States  at  each  of  seven  decennial  censuses.  The 
median  age  is  an  age  such  that  one-half  of  the  population  is 
less  than  it  and  the  other  half  greater  than  it.  Thus  in  1850 
one  half  of  the  total  population  was  under  and  one-half  over 
18.83  years.  The  second  column  of  the  table  shows  that 
there  was  a  gain  of  4.0  years  in  median  age  of  all  classes  of 
population  in  the  50  years  from  1850  to  1900,  the  third 
shows  that  the  gain  in  median  age  of  the  white  population  was 
slightly  greater,  and  the  fourth  shows  that  the  increase  for 

MEDIAN  AGES  FOR  THE  UNITED  STATES 


Year  of  Census. 

All  Classes. 

Whites. 

Colored. 

Native  Whites. 

1850 

18.83 

19.12 

17-33 

i860 

19-38 

19.70 

17-65 

1870 

2O.  14 

20.38 

18.49 

16.71 

1880 

20.86 

21-32 

18.01 

18.30 

1890 

21.42 

21.94 

17.83 

IQ.37 

1900 

22.85 

23-36 

19.70 

20.30 

1910 

24.00 

24.40 

21.  OO 

21.40 

the  colored  population  was  only  about  2. 4  years.  Fair  con- 
clusions cannot  be  drawn  from  the  second  and  third  columns, 
on  account  of  the  influence  of  immigration,  and  accordingly 
the  figures  for  the  native  whites  have  been  added  in  the  last 


44  SANITARY   SCIENCE.  I. 

column  as  far  as  available.  From  these  figures  the  general 
conclusion  follows  that,  aside  from  the  influence  of  immigra- 
tion, the  median  age  of  the  population  of  the  United  States  is 
increasing  at  the  rate  of  about  one  year  for  each  decade. 
While  this  increase  in  median  age  is  undoubtedly  largely  due 
to  the  influence  of  sanitary  science  in  preventing  the  origin  and 
spread  of  disease,  it  is  also  unfortunately  due  in  part  to  a 
diminishing  birth  rate. 

15.  EXERCISES  AND  PROBLEMS. 

The  following  series  of  exercises  and  problems  is  presented 
for  the  use  of  students  in  engineering  colleges,  and  they  will 
prove  of  great  value  in  giving  habits  of  thought  and  investi- 
gation to  all  who  carefully  perform  them.  Some  of  them 
may  be  solved  by  reference  to  dictionaries  and  cyclopedias, 
but  others  will  require  the  consultations  of  the  special  articles 
that  are  mentioned.  The  numerical  problems  of  this  chapter 
involve  only  an  elementary  knowledge  of  arithmetic,  chemis- 
try, and  physics.  The  number  prefixed  is  that  of  the  article 
of  the  text  which  is  especially  related  to  the  exercise  or 
problem. 

i.  What  are  the  meanings  of  the  words  Etiology,  Antitoxine, 
Demography,  Pathology,  Toxicology,  Zymosis  ? 

2  (a)  What  meats  may  be  eaten  and  what  may  not  be  eaten 
according  to  the  sanitary  code  in  Leviticus,  xi,  and  Deuteronomy, 
xiv  ? 

2  (b)  Describe  the  Roman  sewer  called  Cloaca  maxima,  and  the 
Roman  aqueducts  called  Aqua  virgo  and  Aqua  Claudia. 

2  (c)    Read  chapter  vii    of  Volume  II    of  Draper's    Intellectual 
Development  of  Europe;  describe  the  condition  of  English  life  in 
the  latter  part  of  the  thirteenth  century ;  also  how  syphilis  spread 
over  Europe. 

3  (a)  Describe   smallpox,  and  state  the  methods  of  its  prevention 
by  inoculation  and  by  vaccination. 

3  (b)     Is   consumption   an   infectious    disease  ?      See    Harper's 


15.  EXERCISES   AND    PROBLEMS.  45 

Magazine,  March,  1894,  or  Prudden's  Story  of  the  Bacteria  (New 
York,  1889). 

4  (a)  Consult  the  Compendium  of  the  Thirteenth  Census  and  in  the 
Mortality  Statistics  find  the  death  rates  per  thousand  for  the  white, 
colored,  and  total  population. 

4  (b)  How  many  deaths  from  consumption  and  smallpox  occurred  in 
the  United  States  in  1870,  1880,  1890,  1900  and  1910? 

5.  Give  sketches  showing  the  characteristic  forms  of  the  three 
classes  of  bacteria.  What  is  the  name  of  the  germ  that  causes 
typhoid  fever  ? 

6  (a)  If  a  barrel  of  cane  sugar  (C1QH23On)  weighs  342  pounds, 
show  that  the  number  of  pounds  of  carbon,  hydrogen,  and  oxygen 
is  about  144,  22,  and  176. 

6  (b)  What  results  when  nitric    acid  (HNO3)    acts     upon  soda 
(NaOH)  ? 

7  (a)  Consult  Transactions     of    Seventh  International  Congress 
of  Hygiene  and  Demography  (London,  1892),  Vol.  XI,  p.  136,  and 
give  an  abstract  of  Dhurandhar's  account  of  the  sanitary  condition 
of  villages  in  the  Bombay  district  of  India. 

7  (t>)  Give  an  abstract  of  an  article  by  Jordan  and  Richards  on 
the  Nitrifying  Organism  in  Part  II  of  Experimental  Investigations 
by  the  State  Board  of  Health  of  Massachusetts  (Boston.  1890). 

8.  In  an    unventilated    heated  room  where  is  the  warmest  air 
and  where  is  the  air  containing  the  most  carbon  dioxide  ?     Where 
should  fresh  air  be  admitted  and  where  should  the  foul  air  be  taken 
out  in  order  to  give  the  most  effective  ventilation  ? 

9.  Consult    the    recent    reports    of  one    of  the  State  Boards    of 
Health,  and  give  instances  of  disease  communicated  by  bad  water. 

10.  Consult  Part  I  of   Experimental   Investigations  by  the  State 
Board  of   Health  of   Massachusetts   (Boston,    1890),   and  give  an 
account  of  the  work  for  determining  the  normal  chlorine  in  that 
State. 

ii  (a)  If  a  water  has  a  temporary  hardness  of  83  and  a  perma- 
nent hardness  of  42  parts  per  million,  show  that  its  total  hardness 
is  the  same  as  that  caused  by  one  ounce  of  carbonate  of  lime  dis- 
solved in  8  cubic  feet  of  water. 

i !  (b)  In  a  platinum  dish  weighing  43.2675  grams  100  cubic 
centimeters  of  water  are  evaporated  and  it  then  weighs  43.3102 


46  SANITARY   SCIENCE.  I. 

grams.     Show  that  the  total  solids  in  the  water  are  427  parts  per 
million. 

12  (a)  Consult  Rafter's  article  on  Purity  of  Water  Supplies  in 
Vol.  XXI  of  Transactions  American  Society  of  Civil  Engineers,  and 
give  instances  of  trouble  caused  by  Crenothrix  and  Volvox. 

12  (b)  Make  sugar  tests  of  three  samples  of  water  one  of  which 
is  known  to  be  impure  ;  at  the  close  of  the  experiment  observe  also 
the  odor  from  each  sample. 

13  (a)  Consult  Drown's  article    on  Interpretation    of    Chemical 
Analyses  of  Water  in  the  volume  cited  in  question  10,  and  endeavor 
to  interpret  the  analyses  of  normal  and  polluted  waters  given  on 
page  541. 

14  (a)  Consult  the  census  reports  of  the  United  States  and  find  what 
percentage  of  the  total  population  was  over  60  years  of  age  in  1850, 
1860,  1870,  1880,  1890,  1900  and  1910. 

14  (b)  Plot  the.  figures  in  the  first  and  second  columns  of  the  table  of 
median  ages  on  page  43,  and  predict  the  median  ages  for  the  four  classes 
of  the  population  in  1920. 

14  (c)  Consult  Mortality  Statistics  of  the  U.  S.  Census  Bureau  and  find 
what  cities  had  the  highest  death  rates  from  tuberculosis  and  typhoid 
fever  in  1900  and  1910. 

15  (a)  What  are  the  classes  of  the  vegetable  kingdom,  and  to  which 
class  do  bacteria  belong?     What  discoveries  were  made  by  Pasteur? 
What  is  the  antitoxine  method  for  the  cure  of  diphtheria? 

15  (&)  Consult  Stein's  Water  Purification  Plants  and  their  Operation 
(New  York,  1915)  and,  describe  an  "incubator"  for  bacteria  cultures. 

15  (c)  Consult  MacNutt's  Manual  for  Health  Officers  (New  York,  1915) 
and  ascertain  what  human  diseases  are  caused  or  promoted  by  impure 
milk. 


RAINFALL. 


CHAPTER  II. 
WATER   AND    ITS   PURIFICATION. 

16.  RAINFALL. 

The  water  which  has  been  evaporated  from  land  and  ocean 
is  precipitated  in  the  form  of  rain  when  the  temperature  of 
the  atmosphere  is  lowered  by  cooling  winds.  As  the  rain 
falls  it  collects  impurities  from  the  dust  of  the  atmosphere  and 
from  the  surface  of  the  land.  Running  over  the  surface,  it 
forms  swamps,  brooks,  and  rivers;  percolating  into  the  earth, 
it  appears  again  as  springs  and  wells.  Thus  all  water  supply 
is  primitively  due  to  rainfall. 

Rainfall  is  measured  in  inches  or  centimeters  of  vertical 
depth.  A  rain  gage  consists  of  an  open  vessel  for  collecting 
the  falling  water  and  a  cylindrical  glass  tube  of  smaller  cross- 
section  in  which  the  heights  may  be  more  easily  read.  If  the 
area  of  the  cross-section  of  the  tube  be  one-tenth  of  that  of 
the  vessel  one  vertical  inch-  of  water  in  the  vessel  occupies 
ten  inches  in  height  in  the  tube,  and  o.oi  inch  in  the  vessel 
is  o.  10  inch  in  the  tube;  the  graduation  of  the  tube  is  made 
so  as  to  directly  give  the  actual  amount  of  rainfall.  The 
simplest  way  is  to  pour  the  water  from  the  vessel  into  the 
tube  by  the  help  of  a  funnel,  but  in  the  best  work  both  vessel 
and  tube  should  form  one  instrument.  For  precise  observa- 
tions self-registering  gages  are  used,  so  that  the  intensity  of 
rainfall  at  each  instant  may  be  known.  Snow  and  hail  are 
melted  and  the  resulting  water  included  in  the  record  as 
rainfall. 


48  WATER  AND   ITS   PURIFICATION.  II. 

The  frigid  zone  has  the  least  rainfall  and  the  torrid  zone 
the  greatest.  At  the  equator  the  average  annual  rainfall  is 
about  100  inches,  at  latitude  40°  it  is  about  40  inches,  and  at 
latitude  60°  about  20  inches.  There  are,  however,  some 
regions  in  the  temperate  zones  where  practically  no  rain  ever 
falls,  as  in  middle  Egypt,  and  others  where  the  annual  rain- 
fall is  500  inches,  as  in  the  Cossyah  Mountains  of  India.  The 
rainfall  in  any  locality  depends  upon  the  character  of  the 
winds  and  upon  the  neighboring  mountains  and  oceans. 

In  the  United  States  there  is  an  extensive  region,  formerly 
called  the  Great  American  Desert,  where  the  mean  annual 
rainfall  does  not  exceed  15  inches;  this  embraces  the  states 
of  Arizona,  Nevada,  New  Mexico,  Colorado,  Utah,  Wyoming, 
and  Montana,  with  parts  of  adjacent  states.  The  least  annual 
rainfall  for  any  state  is  7f  inches  in  Nevada.  In  all  this  re- 
gion irrigation  is  necessary  for  the  pursuits  of  agriculture, 
the  water  falling  in  the  wet  months  being  impounded  for  use 
in  the  dry  season. 

The  states  having  the  heaviest  annual  rainfall  are  those  on 
the  Gulf  of  Mexico,  the  mean  amount  being  from  50  to  55 
inches;  Florida  and  Louisiana  stand  highest,  with  about  55  and 
54  inches,  respectively,  but  there  are  regions  in  these  states 
where  the  annual  rainfall  exceeds  60  inches.  The  maximum 
annual  rainfall  in  the  United  States  is  found,  however,  near 
Puget  Sound,  in  Oregon  and  Washington,  where  the  mean  is 
30  inches  or  more  per  year,  although  for  the  entire  surface  of 
these  two  states  it  is  only  about  40  inches. 

At  any  place  the  rainfall  in  a  given  year  is  liable  to  vary 
considerably  from  the  mean  for  several  years.  Thus,  the 
mean  annual  rainfall  at  Philadelphia,  Pa.,  for  the  ten  years 
1881-1890  was  39.6  inches,  but  the  highest  annual  rainfall 
was  50.8  inches  in  1890  and  the  lowest  33.4  inches  in  1885, 
the  variations  of  these  from  the  mean  being  28  and  16  per 
cent,  respectively.  Similarly,  at  Denver,  Col.,  the  /ariations 


RAINFALL. 


49 


of  the  maximum  and  minimum  annual  rainfall  from  the  mean 
during  the  same  years  were  40  and  46  per  cent.  Whenever 
the  water  supply  of  a  town  depends  directly  upon  rainfall,  as 
it  does  in  most  cases  where  collecting  and  storage  reservoirs 
are  used,  the  minimum  annual  rainfall  is  a  factor  of  much 
greater  importance  than  the  mean. 


8i        86        88       1890      92        34        M        W      IftN       02       04 

RAINFALL  AT  FOUR  AMERICAN  CITIES. 


06        08      1910 


The  distribution  of  the  rainfall  throughout  the  year  is  very 
different  at^  different  places.  As  a  rough  general  rule  the 
summer  rainfall  is  the  greatest  and  the  autumn  rainfall  the 
least,  but  this  is  reversed  in  a  few  states.  The  following 
table,  abstracted  from  a  larger  one  compiled  by  the  United 
States  Weather  Bureau,  gives  a  general  idea  of  the  mean 
seasonal  variation  in  different  parts  of  the  country.  In 
Massachusetts  the  rainfall  is  equally  distributed  throughout 
the  year,  but  in  California  the  winter  rainfall  is  10  times  as 
great  as  that  in  the  summer.  The  variation  in  rainfall  by 
seasons  and  months  must  be  carefully  regarded  in  planning 


WATER   AND    ITS   PURIFICATION. 


II. 


storage  systems,  and  for  this  purpose  the  rainfall  records  of 
each  special  locality  should  be  obtained  and  discussed. 
MEAN  RAINFALL  IN  DIFFERENT  STATES  AND  SEASONS. 


Spring 

Summer 

Autumn 

Winter 

Annual 

States. 

Rainfall. 

Rainfall. 

Rainfall. 

Rainfall. 

Rainfall. 

Inches. 

Inches. 

Inches. 

Inches. 

Inches. 

Massachusetts, 

ii.  6 

II.4 

II.9 

ii.  7 

46.6 

New  York, 

8-5 

10.4 

9-7 

7-9 

36.5 

Pennsylvania, 

10.3 

12.7 

10.0 

9-5 

42-5 

Virginia, 

10.9 

12.5 

9-5 

9-7 

42.6 

South  Carolina, 

9.8 

16.2 

9-7 

9-7 

45-4 

Alabama, 

14.9 

13.8 

10.0 

14.9 

53-6 

Louisiana, 

13-7 

15.0 

10.8 

14.4 

53-9 

Kentucky, 

12.4 

12.5 

9-7 

ii.  8 

46.4 

Illinois, 

10.2 

II.  2 

9.0 

7-7 

38.1 

Minnesota, 

6.5 

10.8 

5-8 

3-i 

26.2 

Nebraska, 

8.9 

10.9 

4.9 

2.2 

26.9 

Colorado, 

4.2 

5.5 

2.8 

2-3 

14.8 

Montana, 

4.2 

4.9 

2.6 

2-3 

14.0 

California, 

6.2 

0.3 

3-5 

I-I.9 

21.9 

United  States, 

9.2 

10.3 

8.3 

8.6 

36.3 

The  maximum  daily  and  hourly  rainfalls  are  of  importance 
in  some  discussions.  The  maximum  daily  rainfall  for  the 
Atlantic  and  Gulf  states  is  from  8  to  12  inches,  and  for  the 
western  and  Pacific  states  from  4  to  6  inches.  Two  inches  per 
hour  is  a  heavy  precipitation;  on  August  3,  1892,  at  Philadel 
phia,  Pa.,  3.8  inches  fell  in  one  hour. 

17.  EVAPORATION,  RUN-OFF,  AND  PERCOLATION. 

East  of  the  Mississippi  river  the  term  water  year  is  often 
used  in  discussions  of  rainfall  and  run-off;  this  year  begins  on 
December  I,  and  is  divided  into  three  parts.  The  six  months 
December-May  are  called  the  storage  period  when  the  lakes 
and  reservoirs  are  filling;  the  three  months  June- August  ate 
the  growing  period  when  evaporation  is  the  greatest ;  the  three 


I/.     EVAPORATION,  RUN-OFF,  AND  PERCOLATION.     51 

months  September-November  form  the  replenishing  period 
when  a  large  part  of  the  rainfall  percolates  into  the  ground. 
For  the  storage  period  the  evaporation  is  about  one-third,  and 
for  the  growing  period  about  three-fourths,  of  the  rainfall. 

After  the  rain  has  fallen  a  part  of  it  runs  off  into  the  brooks 
and  rivers  and  another  part  percolates  into  the  soil.  Evap- 
oration immediately  begins  both  from  the  land  and  water 
surface,  and  this  continues  until  all  the  rainfall  is  ultimately 
evaporated  into  the  atmosphere,  where  it  is  condensed  into 
clouds  and  falls  again  as  rain.  For  any  particular  watershed 
which  supplies  a  reservoir,  however,  the  evaporation  is  less 
than  the  rainfall,  while  the  run-off  may  be  impounded  for  the 
purposes  of  irrigation  or  water  supply. 

Experiments  on  evaporation  are  made  by  placing  water- 
tight pans  at  the  level  of  the  ground  and  noting  daily  the 
variations  in  depth,  together  with  the  rainfall.  On  the  surface 
of  a  reservoir  or  lake  similar  experiments  may  be  made  by 
floating  boxes.  It  is  found  that  the  evaporation  from  water 
surfaces  is  greater  than  that  from  the  land,  that  it  is  greater 
in  dry  and  desert  regions  than  in  cultivated  ones,  greater  in 
low  lands  than  on  mountains,  and  that  it  increases  with  the 
temperature  of  the  air  and  the  velocity  of  the  wind. 

In  the  Atlantic  states  the  annual  evaporation  from  land 
surfaces  may  be  regarded,  on  the  average,  as  about  40  per 
cent,  and  that  from  water  surfaces  as  about  60  per  cent,  of  the 
annual  rainfall;  in  low  and  level  localities  these  percentages 
are  much  increased,  while  for  high  regions  and  steep  slopes 
they  are  decreased.  In  the  arid  regions  west  of  the  Rocky 
Mountains  the  evaporation  from  water  surfaces  may  be 
several  times  as  great  as  the  rainfall.  In  the  first  region 
nearly  one-half  of  the  annual  rainfall  may  be  utilized  for  a 
water  supply,  while  in  the  second  region  the  percentage  that 
can  be  rendered  available  is  much  smaller. 

The  amounts  of  run-off  and  percolation  depend  upon  the 


52  WATER  AND   ITS   PURIFICATION.  II. 

topography  of  the  country  and  the  nature  of  the  soil.  In  a 
level  country  the  run-off  is  small,  while  on  steep  mountain 
slopes  it  may  be  as  high,  as  80  per  cent  of  the  rainfall.  For 
an  undulating  cultivated  country  the  annual  run-off  usually 
lies  between  40  and  70  per  cent  of  the  annual  rainfall,  while 
the  remainder  goes  into  evaporation  and  percolation.  To 
determine  the  run-off  of  any  watershed  above  a  certain  place 
on  a  stream  the  flow  of  that  stream  is  to  be  measured  by  the 
methods  explained  in  treatises  on  hydraulics,  and  if  such 
observations  be  continued  throughout  a  year  of  average  rain- 
fall a  fair  value  of  the  mean  annual  run-off  is  obtained. 
Should  such  observations  be  impracticable,  an  estimate  may 
be  made  based  on  percentages  of  rainfall  and  evaporation  at 
localities  having  similar  topography  and  climatic  conditions. 
An  example  of  such  estimates  will  be  given  in  Art.  33. 

The  percolation  is  partly  absorbed  by  the  roots  of  plants 
and  trees  growing  on  the  surface,  but  a  large  portion  of  it 
sinks  to  a  greater  depth  and  forms  what  is  called  the  ground 
water.  This  ground  water  is  that  which  appears  in  springs 
and  in  artificial  wells,  and  it  has  a  steady  flow  through  the 
earth  towards  the  streams  and  the  oceans.  When  the 
geologic  conditions  are  favorable  some  of  the  percolation  sinks 
much  deeper  and  forms  those  subterranean  reservoirs  which 
are  called  artesian  waters. 

The  phenomena  of  rainfall,  run-off,  and  percolation  give  rise 
to  three  classes  of  drinking  water.  First,  there  is^rain  water 
which  is  caught  as  it  falls;  second,  the  surface  water  of 
swamps,  brooks,  rivers,  and  lakes;  and  third,  the  ground 
water  of  springs  and  wells.  These  waters  are  now  to  be 
described  and  compared,  their  sources  of  pollution  indicated, 
and  the  methods  for  their  purification  discussed. 

18.   RAIN  WATER. 

Rain  water  is  frequently  collected  and  used  for  a  family 
supply,  particularly  in  country  districts.  The  roof  of  the 


1 8.  RAIN   WATER.  53 

house  forms  the  collection  area,  and  from  this  the  water  is  led 
either  to  a  tank  in  the  garret  or  to  a  cistern  below  the  surface 
of  the  ground.  As  the  roof  is  liable  to  become  covered  with 
dust,  it  is  not  well  to  allow  the  water  to  enter  the  tank  or 
cistern  during  the  first  hour  or  two  of  a  storm.  The  tank  or 
cistern  must  be  provided  with  a  waste-pipe  to  prevent  over- 
flow, but  under  no  circumstances  should  this  be  connected 
with  a  cesspool  or  sewer.  When  due  care  is  used  rain  water 
collected  in  the  country  is  very  pure,  although  those  un- 
accustomed to  it  object  to  its  taste,  and  its  softness  renders 
it  the  best  of  all  waters  for  washing  purposes.  When  col- 
lected in  the  city  it  is  liable  to  contain  smoke,  dust,  and 
organic  matter,  with  the  accompanying  bacteria,  to  a  far 
greater  extent  than  in  the  country. 

Chemical  analyses  of  rain  water  show  that  the  total  solids 
are  lower  than  in  other  kinds  of  water,  say  in  general 
from  20  to  40  parts  per  million.  Free  and  albuminoid 
ammonia  are  always  found,  the  former  being  often  higher  than 
0.050  and  the  latter  usually  less.  Chlorine  may  be  as  low 
as  i.o,  but  is  usually  higher  near  the  coast,  where  salt  is  blown 
in  by  winds  from  the  ocean.  Nitrogen  as  nitrates  is  very  low 
in  amount,  say  0.05  parts  per  million  or  less.  On  the  whole, 
a  chemical  analysis  of  water  from  an  uncontaminated  cistern 
usually  indicates  purity  in  all  directions,  except  that  some- 
times the  free  ammonia  appears  to  run  too  high ;  this  is  not 
necessarily  derived  from  decaying  organic  matter,  but  may 
have  been  washed  out  of  the  atmosphere  by  the  falling  rain. 

The  average  householder  cannot,  however,  be  trusted  to 
exercise  due  care  in  the  collection  of  rain  and  in  maintaining 
the  tank  or  cistern  in  good  order.  A  tank  is  liable  to  become 
infested  with  fungoid  growths,  and  a  cistern  is  liable  to  be 
contaminated  by  household  refuse,  surface  drainage,  or  leak- 
age from  the  soil.  Birds  or  rats  may  sometimes  get  into  the 
roof  pipes,  and  the  organic  matter  from  their  dead  bodies  be 
washed  into  the  tank  or  cistern.  Those  who  have  been 


54  WATER  AND   ITS   PURIFICATION.  II. 

present  at  the  annual  cleaning  of  a  cistern  will  recall  the 
unpleasant  odor  that  usually  attends  that  operation,  and  such 
odor  is  an  indication  of  the  decay  of  organic  matter.  A 
common  custom  in  some  country  districts  is  to  throw  pieces 
of  charcoal  into  the  cistern  in  order  to  alleviate  these  odors, 
but  it  cannot  be  said  that  this  in  any  way  removes  the  sus- 
picion of  impurity.  Although  for  washing  purposes  rain  water 
is  most  excellent  on  account  of  its  lack  of  hardness  and  the 
consequent  economy  in  soap,  it  must  be  concluded  that  it  is 
not  well  to  use  it  for  drinking  water  after  it  has  been  stored 
in  house  tanks  and  cisterns  except  when  great  care  and 
vigilance  have  been  exercised  to  prevent  contamination. 

Snow  collects  matter  from  the  atmosphere  more  readily 
than  rain,  and  hence  water  melted  from  the  first  snow  of  a 
storm  is  more  impure  than  common  rain  water;  likewise,  city 
snow  is  not  as  pure  as  that  of  the  country.  After  snow  has 
fallen  it  absorbs  impurities  from  the  soil  or  from  the  roofs  of 
houses,  so  that  the  amount  of  organic  matter  and  free 
ammonia  may  be  doubled  in  a  day  or  two.  In  general,  water 
produced  by  melting  such  snow  is  not  wholesome,  and  the 
same  may  be  said  of  ice  which  is  formed  from  snow  slush. 

19.  SURFACE  WATERS. 

Surface  waters  include  those  of  swamps,  brooks,  rivers,  and 
lakes,  and  these  differ  greatly  in  regard  to  their  characteris- 
tics. Swamp  water  is  liable  to  be  heavily  charged  with 
vegetable  matter,  but  the  flow  in  brooks  and  rivers  causes  a 
continuous  improvement  in  quality,  and  when  a  lake  is 
reached  the  purest  surface  water  is  found.  This  improvement 
in  quality  is  effected  in  two  ways:  first,  by  settling  or  sedi- 
mentation, which  removes  the  suspended  matter;  and  second, 
by  aeration  or  contact  with  the  air,  whereby  oxygen  is  supplied 
to  decompose  and  destroy  both  the  suspended  and  the  dis- 
solved organic  matter. 


19.  SURFACE  WATERS.  55 

Swamp  water  usually  has  a  high  proportion  of  vegetable 
matter  in  the  total  solids,  and  a  high  proportion  of  albuminoid 
ammonia  is  also  found.  In  boggy  and  peaty  regions  this 
gives  a  brown  color  to  the  water,  but  it  fortunately  happens 
that  the  vegetable  matter  is  in  a  permanent  state  which  resists 
further  decomposition,  so  that  sometimes  these  waters  are 
noted  for  their  keeping  qualities  and  are  well  adapted  to 
being  taken  on  long  sea  voyages.  When  used  for  a  public 
water  supply  the  aeration  due  to  pumping  and  flow  is  apt  to 
cause  this  organic  matter  to  decompose,  and  hence  filtration 
is  necessary.  Swamp  water  has  been  used  at  Long  Branch, 
N.  J.,  Norfolk,  Va.,  and  other  cities  without  unpleasant 
results;  its  softness  renders  it  convenient  for  washing,  but 
brook  or  river  water  is  always  to  be  preferred  for  drinking 
purposes  when  it  can  be  had. 

Brook  water  consists  of  the  run-off  of  the  surface,  of  the 
drainage  of  swamps,  and  of  percolation  from  meadow  and 
springy  land.  It  is  generally  thought  that  the  color  and  taste, 
of  brook  water  give  a  reliable  indication  of  quality,  but  a 
brook  having  its  source  in  farm-yards  or  swampy  pastures  may 
furnish  water  which  is  very  unwholesome,  even  though  it  be 
clear  and  sparkling.  With  steep  slopes  and  rocky  beds  puri- 
fication continually  goes  on,  and  if  further  sources  of  con- 
tamination be  absent  good  potable  water  may  perhaps  be 
found  a  mile  or  two  from  the  suspicious  sources.  Brook 
water  is  soft  except  when  the  flow  comes  from  limestone 
springs,  the  organic  matter  is  usually  lower  than  in  swamp 
water,  while  the  nitrates  are  usually  higher.  It  forms  a 
reliable  public  supply  for  hundreds  of  towns,  being  purified  by 
natural  sedimentation  in  collecting  reservoirs  and  sometimes 
by  artificial  filtration. 

A  river  is  formed  by  many  brooks,  and  the  quality  of  river 
water  differs  mainly  from  that  of  brook  water  in  the  higher 
proportion  of  inorganic  matter  which  has  been  collected  from 
the  soil  in  the  flow.  A  river  having  towns  upon  its  banks  is 


56  WATER  AND   ITS   PURIFICATION.  II. 

liable  to  become  polluted  by  the  drainage  and  sewage  that 
run  into  it,  and  at  present  one  of  the-  important  sanitary 
problems  is  how  to  dispose  of  the  refuse  of  towns  without 
polluting  the  streams.  In  Europe  this  subject  has  received 
much  attention,  and  the  matter  that  may  be  thrown  into  rivers 
is  regulated  by  law;  in  this  country  some  states  have  also 
made  enactments  which  in  time  will  no  doubt  be  perfected 
and  enforced.  The  chemical  analysis  of  water  collected  below 
a  town  which  discharges  sewage  into  a  river  shows  a  higher 
proportion  of  chlorine  than  is  found  above  the  town,  and  the 
number  of  bacteria  will  also  in  general  be  much  greater. 
River  water  is  improved  by  sedimentation  in  reservoirs,  but 
if  very  impure  it  must  be  treated  by  artificial  filtration  before 
delivering  it  to  the  distributing  basins. 

Lakes  are  natural  reservoirs  which  collect  the  water  of 
brooks  and  rivers.  When  of  large  size  they  furnish  an  excel- 
lent supply,  for  both  sedimentation  and  aeration  have  had 
opportunity  to  remove  the  organic  matter.  The  water  of  a 
lake  may  be  polluted,  however,  by  the  refuse  of  towns  or  by 
the  discharge  of  sewage  into  it,  so  that  contamination  may 
extend  to  a  considerable  distance  from  the  shores;  at  Chicago, 
for  instance,  the  supply  is  collected  in  cribs  four  or  five  miles 
from  the  lake  shore  and  carried  in  tunnels  to  the  city  in  order 
to  secure  uncontaminated  water.  In  small  lakes  and  ponds 
the  liability  to  pollution  is  greater  still,  and  hence  filter  gal- 
leries are  frequently  used  to  insure  purification. 

It  should  be  noted  that  the  quality  of  water  from  any  given 
stream  or  lake  undergoes  systematic  variations  with  the 
changes  of  the  seasons.  In  late  winter  and  early  spring  the 
melting  ice  and  snow  cause  the  maximum  run-off  of  the  year, 
and  the  streams  become  swollen  and  foul  with  organic  and 
inorganic  matter.  In  summer  the  flow  becomes  normal  and 
the  highest  degree  of  purity  obtains;  in  autumn  the  flow  is  a 
minimum  and  liability  to  pollution  is  greater  than  in  the 
summer.  Even  in  a  pond^ whose  surface  does  not  vary  greatly 


20.  GROUND   WATERS.  57 

in  height  there  are  variations  due  to  the  influence  of  wind  and 
temperature.  It  was  shown  by  Drown  in  1891  that  in  deep 
ponds  and  reservoirs  a  stagnant  layer  containing  unoxidized 
organic  matter  is  formed  during  the  summer,  and  that  this 
rises  to  the  surface  late  in  the  fall  when  the  higher  layers 
become  cooled ;  a  vertical  circulation  then  occurs  with  more 
or  less  regularity  until  spring,  when  the  stagnant  layer  begins 
to  form  again.  Hence  both  river  and  lake  waters  are  liable 
to  be  of  variable  quality  from  fall  until  spring,  and  the  neces- 
sity for  artificial  purification  is  greater  then  than  during  the 
summer  season. 

20.-  GROUND  WATERS. 

The  water  of  springs  and  wells  comes  from  that  part  of  the 
rainfall  which  has  percolated  into  and  through  the  soil.  In 
the  upper  layers  of  the  soil  a  large  part  of  the  organic  matter 
is  removed  by  the  action  of  bacteria  and  absorbed  by  the 
growing  vegetation.  As  the  percolation  extends  downward 
mineral  matter  is  generally  taken  up,  so  that  ground  water  is 
harder  than  surface  water.  In  good  spring  or  well  water  the 
total  solids  may  be  as  high  as  100  parts  per  million,  but  very 
little  of  this  is  organic  matter;  the  ammonias  and  nitrates  are 
very  low,  while  the  amount  of  chlorine  should  not  exceed  the 
normal  for  the  region.  If  both  chlorine  and  nitrates  are  found 
high  it  is  an  indication  of  sewage  contamination. 

Water  rises  in  springs  from  the  hydrostatic  pressure  of  a 
body  of  water  which  fills  the  soil  below  a  certain  depth.  This 
body  of  water  has  a  slow  motion  through  the  soil  towards  the 
streams  and  the  ocean,  and  it  has  a  more  or  less  definite 
surface  which  slopes  in  the  direction  of  flow.  In  the  sandy 
soil  of  Long  Island  the  slope  of  the  surface  of  this  ground 
water  is  about  10  feet  per  mile,  but  in  clayey  or  rocky  soils 
the  slope  is  not  as  great.  The  depth  of  this  water  surface 
below  the  level  of  the  earth  varies  in  different  seasons,  and 


WATER   AND    ITS   PURIFICATION. 


II. 


also  in  years  of  different  rainfall.  When  the  topography  of 
the  region  is  such  that  this  body  of  ground  water  is  inter- 
cepted a  spring  results  and  clear  water  bubbles  up  at  the  foot 
of  a  hillside. 

Well  water  is  merely  ground  water  which  is  intercepted  by 
sinking  a  pit  into  the  earth.  If  the  draft  be  great  the  surface 
of  the  ground  water  around  the  well  assumes  the  conoidal 
shape  indicated  in  the  figure,  and  if  it  be  very  great  the  well 


OPEN  WELL  IN  GROUND  WATER. 

may  become  dry.  When  many  wells  are  sunk  near  together 
the  surface  of  the  ground  water  becomes  permanently  lowered 
and  it  may  be  difficult  to  obtain  the  supply  desired.  This 
has  been  markedly  the  case  at  Brooklyn,  N.  Y. ;  at  a  well 
sunk  in  1869  the  ground-water  level  was  lowered  five  feet  in 
eight  years  of  pumping,  so  that  the  construction  of  other  wells 
became  necessary,  and  the  same  phenomena  continued  to 
prevail  at  all  of  these,  until  finally  many  wells  at  considerable 
distances  from  the  city  are  required  to  maintain  the  supply. 

Driven  wells  are  pointed  iron  tubes  with  holes  near  the 
lower  ends  which  are  sunk  into  the  soil  until  they  pierce  the 
ground-water  level.  The  water  is  raised  by  a  suction-pump  at 
the  top  of  the  tube,  or  sometimes  several  tubes  are  connected 
to  one  pump;  of  course,  water  cannot  be  raised  by  this  method 
higher  than  about  30  feet  above  the  ground-water  level. 
There  is  nothing  mysterious  in  a  driven  well,  as  many  sup- 
pose, nor  can  any  more  water  be  obtained  from  it  than  from 
an  open  one  by  the  same  expenditure  of  work. 


20. 


GROUND   WATERS. 


59 


House  wells  are  liable  to  become  polluted  by  the  drainage 
of  outhouses  and  cesspools;  the  older  the  well  the  greater  is 
the  danger,  for  the  surrounding  soil  is  apt  to  become  fouler 
year  by  year,  and  finally,  when  an  unusual  lowering  and  sub- 
sequent inflow  of  ground  water  occurs,  contamination  results. 
In  numerous  cases  boards  of  health  have  found  it  necessary 
to  order  wells  to  be  filled  up  on  account  of  the  disease  and 
death  which  they  have  caused. 

Deep  wells  sunk  from  100  to  300  feet  in  rock  furnish  water 
for  towns  as  also  for  houses  and  manufactories.  Here  the 
ground  water  pervades  the  fissures  of  the  rock  and  is  inter- 
cepted by  the  well;  it  is  usually  raised  to  the  surface  by  a 
force  or  lift  pump,  which  is  operated  by  a  plunger  from  an 
engine  on  the  surface.  The  quality  of  such  water  does  not 
differ  essentially  from  that  of  the  surrounding  ground  water, 
except  in  the  larger  proportion  of  mineral  matter. 

Artesian  water  comes  from  a  well  carried  down  to  pierce  a 
water-bearing  stratum  whose  outcrop  is  at  a  considerable  dis- 
tance from  the  well.  Thus  in  the  figure  the  water  falling  on 


ARTESIAN  WELL. 

the  outcrop  A  is  confined  by  the  geologic  conditions  to  the 
stratum  AB,  and  rises  through  the  well  BC  by  virtue  of  the 
hydrostatic  pressure.  In  some  cases  the  water  spouts  up 
above  the  top  of  the  well,  while  in  others  pumping  is  neces- 
sary. Many  wells  of  this  kind  have  been  sunk  in  the  United 
States;  one  at  Charleston,  S.  C.,  is  1260  feet  deep,  and  its 
water  level  rises  and  falls  with  the  tide,  although  not  simul- 
taneously; at  St.  Louis,  Mo.,  there  are  two  whose  depths  are 
2199  and  3843  feet.  Artesian  waters  are  generally  so  highly 


60  WATER  AND   ITS   PURIFICATION.  II. 

impregnated  with  metallic  salts  as  to  be  unsuited  for  domestic 
uses,  the  total  solids  being  often  from  500  to  1000  parts  per 
million.  The  «chlorine,  ammonias,  and  nitrates  are  also  high, 
but  these  do  not  indicate  contamination,  as  in  surface  and 
ground  waters.  The  main  use  of  artesian  water  is  in  manufac- 
tories, where  hardness  and  mineral  salts  are  not  objectionable, 
but  in  some  cases  it  is  also  collected  for  the  supply  of  towns. 

21.  RESERVOIRS. 

The  surface  water  of  swamps  and  brooks  and  the  ground 
water  of  springs  is  collected  in  reservoirs  for  storage  and  dis- 
tribution. River  and  lake  water  is  also  pumped  into  reser- 
voirs and  tanks,  or  it  is  often  delivered  directly  into  the  pipes 
without  the  use  of  reservoirs.  The  use  of  reservoirs  not  only 
enables  a  sufficient  supply  to  be  maintained,  but  also  affords 
opportunity  for  clarifying  and  purifying  the  water. 

Reservoirs  for  irrigation  were  extensively  built  in  Egypt 
and  India  in  ancient  times.  Lake  Maeris  in  Egypt,  con- 
structed about  2000  B.C.,  is  said  to  have  been  413  miles  in 
circumference.  The  Romans  built  reservoirs  for  supplying 
water  to  their  aqueducts,  selecting  the  water  of  springs  in 
preference  to  surface  water.  In  India  there  are  thousands  of 
reservoirs  still  in  operation  which  were  constructed  in  early 
times  for  purposes  of  irrigation;  one  of  the  modern  reservoirs 
has  an  earthen  dam  12  700  feet  long  and  a  storage  aiea  of 
4.2  square  miles. 

Collecting  and  storage  reservoirs  are  those  that  impound 
the  water  of  streams,  while  distributing  reservoirs  are  those 
whose  water  is  supplied  either  from  storage  reservoirs  or  by 
pumping  from  rivers  and  lakes.  From  the  distributing  reser- 
voir the  water  goes  to  the  town  through  mains,  under  the 
action  of  gravity;  in  some  cases,  however,  the  same  reservoir 
may  serve  both  for  storage  and  for  distribution.  A  collecting 
reservoir  is  usually  made  by  constructing  a  dam  across  a 


21.  RESERVOIRS.  6 1 

valley,  thus  creating  an  artificial  lake,  while  distributing 
reservoirs  are  made  by  forming  an  excavation  on  a  hill.  The 
engineering  features  of  these  constructions  are  to  be  described 
in  the  next  chapter,  while  here  those  points  are  to  be  dis- 
cussed which  are  important  for  insuring  the  purity  of  the 
water. 

A  collecting  reservoir  formed  by  throwing  a  dam  across  a 
valley  impounds  the  run-off  of  the  water  shed  above  that  dam. 
It  is  very  desirable  that  the  area  to  be  covered  by  the  im- 
pounded water  should  be  carefully  cleaned;  all  trees  and 
bushes  should  be  removed,  and  if  the  upper  layer  of  the  soil 
contains  vegetable  matter  it  should  also  be  excavated  and 
carted  away.  Neglect  of  these  precautions  has  frequently 
caused  the  water  to  be  of  bad  quality,  on  account  of  the 
absorption  of  decaying  organic  matter.  For  instance,  at 
Wilkesbarre,  Pa.,  a  swampy  region  was  in  1891  turned  into  a 
storage  reservoir  by  the  construction  of  a  dam  and  cleaning 
was  imperfectly  done;  the  poor  quality  of  the  water  rendered 
an  extensive  filtration  plant  necessary,  but  even  this  could  not 
satisfactorily  clarify  the  water,  so  that  later  the  entire  system 
was  abandoned  and  a  supply  for  the  city  obtained  from 
another  source.  Considerations  of  the  character  of  the  water 
entering  the  reservoir,  of  its  depth  in  the  reservoir,  and  of  the 
treatment  it  is  to  receive  before  being  delivered  to  consumers 
have  since  1905  sometimes  limited  the  extent  to  which  such 
cleaning  is  advisable. 

The  bed  of  a  storage  reservoir  should  hence,  if  possible,  be 
formed  of  clean  gravelly  earth  or  of  rock.  Its  banks  should 
be  free  from  all  rubbish  that  is  liable  to  be  washed  into  the 
water  in  times  of  storm,  and  a  certain  degree  of  sanitary 
patrol  should  be  established  around  it.  In  most  states  the 
law  provides  for  the  proper  punishment  of  persons  who 
pollute  a  reservoir  by  throwing  organic  matter  into  it  or  by 
bathing  in  its  water,  but  the  enforcement  of  these  laws  is  far 
from  universal.  Moreover,  unintentional  pollution  is  liable 


62  WATER  AND   ITS   PURIFICATION.  II. 

to  occur  from  farmhouses  and  barns  situated  on  the  water- 
shed, and  this  is  to  be  prevented  only  by  a  regular  system  of 
inspection.  Probably  the  most  complete  system  of  sanitary 
patrol  of  a  reservoir  in  the  United  States  is  that  exercised  at 
Hemlock  Lake,  which  supplies  Rochester,  N.  Y.t  the  refuse 
of  all  farmhouses  around  the  lake  being  systematically  carried 
away  and  every  precaution  taken  to  prevent  contamination. 

A  distributing  reservoir  is  smaller  than  a  collecting  one,  and 
usually  its  bottom  and  sides  are  made  of  concrete,  in  order  to 
prevent  leakage.  The  mains  enter  it  in  a  gate-house,  which 
is  often  so  arranged  that  the  water  may  be  taken  from  differ- 
ent depths  below  the  surface.  There  is  also  a  waste  pipe 
running  out  from  the  bottom,  which  is  used  to  entirely  empty 
the  reservoir  and  to  remove  the  mud  deposit  that  may  have 
formed  in  it.  A  similar  method  of  cleaning  out  the  deposits 
in  a  collecting  reservoir  may  also  be  used,  provided  that  the 
supply  of  the  town  is  not  impaired  by  emptying  it.  Organic 
matter  in  a  distributing  reservoir  is  far  more  dangerous  than 
in  a  collecting  one,  and  hence  the  access  of  the  public  to  it 
should  be  absolutely  prevented  by  means  of  an  effective 
enclosure. 

The  quality  of  water  in  a  reservoir  is  always  improved  by 
putting  a  roof  over  it,  but  this  is  only  practicable  when  the 
area  is  small.  The  roof  protects  the  water  from  sunlight,  and 
hence  renders  its  temperature  more  uniform  and  retards  the 
growth  of  diatoms  and  other  vegetable  organisms.  As  in- 
direct advantages  the  evaporation  is  lessened  and  pollution  by 
birds  is  prevented.  At  Paris  there  is  a  covered  reservoir 
whose  size  is  136  X  272  meters,  at  London  there  are  two, 
and  at  Naples  there  is  an  underground  reservoir  in  rock 
galleries  on  a  hill. 

Analyses  of  reservoir  water,  made  monthly  or  at  shorter 
intervals,  are  of  great  value  in  giving  knowledge  of  the 
changes  that  go  on  with  the  progress  of  the  seasons,  in  giving 


22.  SEDIMENTATION  AND  AERATION.  63 

warnings  of  danger,  and  in  showing  the  effect  of  improve- 
ments in  methods  of  collection.  A  single  isolated  analysis, 
on  the  other  hand,  is  of  little  value,  as  it  gives  no  opportunity 
for  comparisons. 

22.  SEDIMENTATION  AND  AERATION. 

Sedimentation  and  aeration  are  two  processes  by  which 
nature  purifies  water.  Sedimentation  or  settling  occurs  when 
a  body  of  water  is  kept  quiet,  so  that  the  suspended  matter 
may  slowly  settle.  Aeration  is  bringing  the  water  into  con- 
tact with  air,  so  that  its  oxygen  may  enable  the  bacteria  to 
decompose  both  the  suspended  and  dissolved  organic  matter. 
These  processes  must  be  carried  on  at  different  times,  since 
aeration  involves  the  agitation  of  the  water. 

Sedimentation  is  consequently  going  on  in  all  collecting 
and  distributing  reservoirs.  The  force  of  gravity  acting  on 
the  suspended  organic  and  inorganic  matter  causes  it  to 
slowly  fall,  provided  that  its  specific  gravity  is  greater  than 
that  of  the  water.  The  downward  force  on  any  particle  is 
the  difference  between  its  weight  and  the  weight  of  an  equal 
volume  of  water,  and  it  is  clear  that  this  may  be  very  small 
for  organic  matter,  and  that  hence  the  velocity  of  fall  is  also 
small.  Moreover,  the  theory  of  the  descent  of  a  small  spheri- 
cal body  in  a  resisting  medium  shows  that  the  velocity  soon 
becomes  uniform  and  that  it  varies  as  the  square  root  of  the 
diameter  of  the  body.  Accordingly,  very  small  particles  of 
silt  fall  very  slowly  in  water  and  take  a  long  time  to  reach  the 
bottom  of  the  reservoir.  So  fine  is  the  division  of  the  silt  in 
the  water  of  the  Missouri  River  that  bottles  of  it  have  been 
kept  for  years  without  becoming  fully  clarified.  To  secure 
the  quickest  rate  of  sedimentation  it  is  plain  that  the  water 
should  be  very  quiet  and  that  its  depth  should  not  be  too 
great. 

The  process  of  sedimentation  consists  mainly  in  the  fall  of 


64  WATER  AND   ITS  PURIFICATION.  IL 

the  suspended  inorganic  matter,  but  this  in  descending  also 
drags  down  some  of  the.  suspended  organic  matter  with  it. 
As  the  organic  matter  is  closely  of  the  same  specific  gravity 
as  water,  the  velocity  of  fall  of  a  grain  of  silt,  whose  specific 
gravity  may  be  double  that  of  water,  is  retarded  on  striking  a 
particle  of  organic  matter,  and  thus  another  reason  is  apparent 
why  the  process  of  sedimentation  is  so  slow.  But  if  sufficient 
time  be  afforded  a  large  proportion  of  the  suspended  inorganic 
matter  will  ultimately  be  precipitated,  with  the  result  of  ren- 
dering the  water  clearer  and  more  suitable  for  domestic  uses. 

Aeration  consists  in  causing  the  water  to  dissolve  oxygen 
out  of  the  air.  This  oxygen  immediately  attacks  both  the 
suspended  and  dissolved  organic  matter  in  the  manner 
explained  in  Art.  6,  and  the  process  of  nitrification  proceeds 
until  the  ammonia  has  disappeared  by  being  transformed  into 
nitrates.  This  process  goes  on  to  a  greater  or  less  extent  in 
all  impure  water  to  which  sufficient  oxygen  is  supplied,  pro- 
vided such  water  contains  in  solution  potash,  soda,  and  other 
metallic  alkalies.  Sedimentation  purifies  the  water  by  remov- 
ing suspended  matter,  and  a  large  part  of  this  is  inorganic 
matter  only,  but  aeration  purifies  it  by  removing  both  the 
suspended  and  the  dissolved  organic  matter. 

A  large  collecting  reservoir  will  have  its  surface  agitated  at 
times  by  winds,  and  thus  considerable  air  is  absorbed  by  the 
upper  layers  of  the  water.  In  transferring  the  water  from  a 
collecting  to  a  distributing  reservoir  there  is  frequently  found 
the  opportunity  to  give  it  more  satisfactory  aeration.  If  the 
transfer  be  made  by  an  open  canal,  this  can  be  built  so  that 
there  may  be  one  or  two  falls  where  the  water  flows  over 
rocks  and  is  broken  up  into  foam.  If  a  water  main  be  used, 
the  terminus  at  the  distributing  reservoir  can  be  made  so  as 
to  throw  the  water  up  in  fountain  spray  and  thus  secure  a 
thorough  admixture  of  air.  The  experience  at  Reading,  Pa., 
in  1880-85,  may  be  cited  as  showing  the  advantage  of  the 
second  method.  A  portion  of  the  storage  at  Antietam  Lake 


22.  SEDIMENTATION  AND   AERATION.  6$ 

was  directly  distributed  to  the  city,  while  the  remainder  was 
carried  to  distributing  reservoirs  and  entered  them  by  foun- 
tains which  threw  the  water  to  a  height  of  75  feet.  In  the 
part  of  the  city  served  directly  from  the  lake  disagreeable 
odors  and  tastes  were  observed  in  August  of  each  year,  but 
in  the  sections  served  from  the  distributing  reservoirs  the 
water  was  entirely  free  from  such  unpleasantness.  The  offen- 
sive odor  and  taste  were  doubtless  due  to  the  decay  of  diatoms 
or  other  vegetable  growths,  but  the  aeration  at  the  distribut- 
ing reservoirs  had  completely  oxidized  the  decaying  matter. 

The  following  chemical  analyses  will  give  a  general  idea  of 
the  changes  that  occur  in  brook  water  by  storage  and  sedi- 
mentation. The  reservoir  in  question  is  one  at  Springfield, 
Mass.,  and  the  analyses  are  the  mean  of  several  made  by  the 
Massachusetts  State  Board  of  Health  in  April  and  May,  1889. 
The  samples  of  wa£er  from  the  brooks  were  collected  where 
they  entered  the  reservoir,  and  those  from  the  reservoir  itself 
were  collected  near  the  middle  and  at  a  depth  of  six  feet 
below  the  surface.  The  figures  express  parts  per  million: 

Brooks.  Reservoir. 

Total  Solids,  33.9  23.8 

Organic  Matter,  13.9  9.5 

Inorganic  Matter,  20.0  14.3 

Chlorine,  0.8  i.o 

Free  Ammonia,  0.017  0.002 

Albumenoid  Ammonia,  0.163  0.190 

Nitrogen  as  Nitrates,  0.023  0.023 

Nitrogen  as  Nitrites,  0.004  0.003 

Here  the  total  solids,  both  organic  and  inorganic,  are 
diminished,  and  the  general  increase  in  purity  is  indicated  by 
the  decrease  in  free  ammonia.  This  reservoir,  it  may  be 
noted,  has  always  given  more  or  less  trouble  by  odors  due  to 
decaying  algae,  and  it  may  be  that  the  presence  of  living  algae 
prevented  the  increase  in  nitrates  which  would  naturally  be 
expected. 


66  WATER  AND  ITS  PURIFICATION.  [II. 


23.  NATURAL  FILTRATION. 

Sedimentation,  aeration,  and  filtration  are  the  three  meth- 
ods by  which  nature  purifies  water.  The  word  filtration 
means  primitively  screening  or  straining,  but  when  applied  to 
water  purification  it  has  a  much  more  extended  signification. 
It  means  not  only  the  removal  of  the  suspended  matter  by 
screening  or  straining,  but  the  removal  of  the  dissolved 
organic  matter  by  nitrification  which  is  produced  by  bacteria 
in  the  presence  of  oxygen.  In  the  article  on  ground  waters 
a  general  description  of  this  process  was  given,  but  it  is  well 
to  consider  it  in  fuller  detail,  as  the  theory  is  of  great  impor- 
tance in  the  discussion  of  methods  of  artificial  filtration. 

The  rainfall  which  percolates  into  the  earth  collects  im- 
purities from  the  surface,  some  of  which  are  screened  out  in 
passing  through  the  upper  layer  of  the  soil,  while  others 
remain  in  solution.  The  interstices  of  the  soil  are  filled  with 
air  which  has  entered  prior  to  the  fall  of  rain,  and  the  water 
thus  becomes  charged  with  dissolved  oxygen.  Each  particle 
of  sand  or  earth  is  surrounded  by  a  film  of  water  which  is 
subject  to  a  slow  downward  motion  from  the  pressure  above 
it,  and  in  these  thin  films  the  bacteria  work  with  great  activity 
in  decomposing  the  organic  matter.  As  the  water  descends 
in  the  soil  more  and  more  organic  matter  becomes  nitrified, 
but  the  process  ceases  after  a  depth  of  four  or  five  feet  is 
reached,  because  the  difficulty  of  getting  air  prevents  the 
bacteria  from  carrying  on  their  useful  work.  The  descent  of 
the  water  continues,  however,  until  the  level  of  the  ground 
water  is  reached,  and  in  this  body  of  ground  water  more  or 
less  sedimentation  goes  on,  which  removes  some  of  the  sus- 
pended matter  still  remaining,  while  the  dissolved  inorganic 
matter  increases  by  absorption  of  metallic  salts  from  the 
earth.  This  is  the  process  by  which  impure  surface  water  is 
converted  into  the  clear  water  of  springs  and  wells. 


23.  NATURAL   FILTRATION.  6/ 

A  water  supply  derived  from  ground  water  has  hence  been 
purified  by  natural  filtration.  The  amount  of  chlorine  in  the 
surface  water  is  not  decreased  by  the  filtration,  but  if  an 
increase  is  observed  this  is  derived  from  the  soil.  If  the 
normal  chlorine  in  a  spring  or  well  water  is  found  to  increase, 
this  is  almost  certainly  due  to  pollution  from  sewage,  as  all 
sewage  contains  salt  which  is  derived  from  the  food  of  men. 

Public  water  supplies  of   ground  water  may  be  obtained 
from  open  or  driven  wells,  as  explained  in  Art.  20,  and  also 
by  means  of  filter  galleries  or  tun- 
nels.    The  figure  shows  a  filter  gal-     ;:V^Vv%^^/;cy^i^^';l'^=;V5: 
lery  in  the  ground  which  is  covered    ^-^^.v^^^ftUffi^^WA^ 
with  an  arch  and  has  an  open  bottom    £?jj^^/:/£££^^$i$$ 
through    which    the    ground    water    -^i 
enters;     in    water-bearing    rock    an     |gj 
artificial  arch  may  not  be  required.     £$] 
The  city  of  Dubuque,  la,,   derives 

its  supply  from  a  filter  gallery  a  mile  FlLTER  GALLERY- 

long  driven  horizontally  into  rock  at  a  depth  of  more  than 
100  feet  below  the  surface  of  a  bluff.  Filter  galleries  are  also 
constructed  along  the  banks  of  rivers,  so  that  the  river  water 
may  percolate  into  them  and  become  purified  in  its  passage 
through  the  soil,  but  in  such  cases  a  part  of  the  supply  is  apt 
to  be  ground  water;  such  galleries  have  been  built  at  Brook- 
line,  Mass.,  Columbus,  O.,  and  many  other  places.  A  filter 
basin  is  similar  in  principle  to  a  filter  gallery,  but  it  usually 
has  an  open  top  and  is  thus  merely  a  very  large  well.  The 
object  of  all  such  constructions  is  to  collect  water  which  has 
been  purified  by  the  method  of  natural  filtration. 

The  following  figures,  which  give  average  results  of  a  large 
number  of  chemical  analyses  made  by  the  State  Board  of 
Health  of  Massachusetts  in  1887-89,  show  the  effect  of 
natural  filtration  at  Framingham,  Mass.  The  source  of  sup- 
ply is  a  filter  gallery  which  receives  its  water  from  a  pond, 
part  of  the  gallery  being  underneath  the  pond  and  the  water 


68  WATER   AND   ITS   PURIFICATION.  II. 

entering  through  the  bottom,  as  shown  in  the  preceding  figure ; 
in  order  to  enter  the  gallery  the  pond  water  must  pass  through 
at  least  five  feet  of  earth.  All  figures  are,  as  usual,  expressed 
in  parts  per  million: 

Pond.       Filter  Gallery. 

Hardness,  16  30 

Total  Solids,  51.0  59.3 

Organic  Matter,  16.3  9.0 

Inorganic  Matter,  34.7  50.3 
Chlorine,                                           4.0  4.5 

Free  Ammonia,  0.047  o-oS1 

Albumenoid  Ammonia,  0.262  0.084 

Nitrogen  as  Nitrates,  0.158  0.272 

Nitrogen  as  Nitrites,  0.003  0.003 

Here  the  effect  of  the  purification  is  seen  in  the  decrease 
of  the  organic  matter  and  ammonias  and  in  the  increase  of  the 
nitrates.  The  increase  in  hardness  and  chlorine  indicates 
either  that  some  ground  water  reached  the  gallery  or  that  the 
filtering  soil  contained  calcium  carbonate  and  sodium  chloride. 
The  permanence  of  the  nitrites  shows  that  the  purification 
was  not  fully  satisfactory. 


24.  ARTIFICIAL  METHODS  OF  PURIFICATION. 

The  three  methods  by  which  nature  purifies  water  are  sedi- 
mentation, aeration,  and  filtration,  and  in  the  preceding 
articles  it  has  been  shown  how  these  are  used  by  man  in  allow- 
ing subsidence  in  reservoirs,  in  causing  air  to  be  dissolved  by 
the  water,  and  in  collecting  ground  water  which  has  been 
filtered  by  passage  through  the  earth.  There  are,  however, 
other  methods  used  by  man;  a  brief  classification  of  these 
will  here  be  given,  and  the  most  important  of  them  will 
receive  fuller  discussion  in  subsequent  articles. 

Distillation  of  water  consists  in  turning  it  into  steam,  which 
is  again  condensed  into  water.  This  is  undoubtedly  the  most 


24.  ARTIFICIAL  METHODS  OF  PURIFICATION.  69 

effective  process  of  purification,  but  it  is  so  expensive  that  it 
is  only  to  be  used  in  exceptional  cases,  as  on  steamships;  most 
of  the  vessels  of  the  United  States  navy  are  provided  with 
apparatus  for  distilling  salt  water.  The  heat  destroys  the 
bacteria,  and  the  evaporation  leaves  both  suspended  and  dis- 
solved solid  matter  behind,  with  the  result  that  distilled  water 
is  the  purest  obtainable,  although  its  lack  of  taste  renders  it 
somewhat  unpalatable. 

Boiling  is  an  effective  method  for  the  purification  of  water 
if  it  be  continued  for  half  an  hour  or  more,  as  the  bacteria  are 
killed  by  the  heat  and  hence  the  organic  matter  is  rendered 
harmless.  It  is  said  that  the  boiling  of  drinking  water  is  a 
widespread  custom  in  China  and  Japan,  and  it  may  perhaps 
be  partly  due  to  this  that  these  countries  are  free  from  the 
frightful  epidemics  which  are  so  common  in  India.  Boiling 
is  also  an  expensive  process,  and  cannot  be  carried  out  except 
in  a  household  where  fire  is  needed  for  other  purposes. 

Hard  water  frequently  requires  to  be  softened  before  it  can 
be  economically  used  for  washing,  and  in  steam-boilers  its  use 
is  objectionable  on  account  of  the  carbonate  of  lime  which  is 
deposited.  Clark's  process  for  softening  water  of  temporary 
hardness  is  to  add  limewater  (CaO,H2O);  this  unites  with  the 
free  carbon  dioxide  (CO3)  in  the  water  to  form  calcium  car- 
bonate (CaCO3),  which  is  immediately  precipitated  and  drags 
down  with  it  the  calcium  carbonate  in  solution.  If  the  hard- 
ness be  permanent,  or  due  to  calcium  sulphate  (CaSO4),  it  is 
necessary  to  add  sodium  carbonate  (NaaCO3);  the  combination 
of  these  produces  calcium  carbonate  (CaCO3)  and  sodium  sul- 
phate (Na,SO4),  and  the  former  of  these  is  precipitated.  In 
England  many  public  water  supplies  have  such  a  high  degree 
of  temporary  hardness  that  the  limewater  process  is  used  on 
a  large  scale.  In  America,  however,  a  public  water  supply 
is  rarely  so  hard  as  to  require  such  treatment,  and  in  house- 
holds sodium  carbonate  is  generally  used  for  softening  waters 
both  of  temporary  and  permanent  hardness. 


70  WATER  AND  ITS  PURIFICATION.  II. 

Chemical  precipitation  is  also  used  to  clarify  water,  particu- 
larly in  connection  with  methods  of  mechanical  filtration. 
Electrical  methods  of  purification  may  be  classed  with  the 
chemical  ones,  and  both  will  be  discussed  in  Art.  25. 

Household  filters  depend  for  their  efficiency  mostly  upon 
the  screening  or  straining  action,  and  do  not  use  the  true 
filtration  principle  of  removing  organic  matter  by  nitrification. 
Some  of  these  will  be  described  in  Art.  26. 

Mechanical  filters  are  those  that  force  water  through  sand 
or  other  earthy  material;  these  employ  the  nitrification  prin- 
ciple only  to  a  slight  extent.  In  Art.  27  one  or  two  of  the 
most  common  kinds  will  be  explained. 

Artificial  filtration  through  beds  of  sand,  carried  on  slowly 
and  intermittently,  so  as  to  imitate  the  process  of  natural 
filtration,  is  the  most  effective  method  of  purifying  an  unsat- 
isfactory public  water  supply.  The  construction  and  opera- 
tion of  such  filter  beds  will  be  discussed  and  illustrated  in 
Arts.  28  and  29. 

25.  CHEMICAL  AND  ELECTRICAL  METHODS. 

All  chemical  treatment  which  causes  precipitation  also 
purifies  the  water  of  suspended  organic  matter.  Thus,  the 
addition  of  limewater  to  water  containing  calcium  carbonate 
causes  this  to  be  precipitated,  and  it,  in  descending,  drags 
down  a  considerable  proportion  of  the  suspended  matter. 
Most  of  the  common  chemical  methods  of  purifying  water 
depend  upon  this  principle. 

Alum  is  one  of  the  best-known  precipitants.  This  is 
a  double  salt  of  aluminum  and  potassium  sulphates 
(Ala(SO4)3.K2SO4),  and  when  added  to  water  (H,O)  contain- 
ing calcium  carbonate  (CaCO3)  in  solution  there  results 
carbon  dioxide  (CO2),  calcium  sulphate  (CaSO4),  potassium 
sulphate  (KaSO4),  and  aluminum  hydroxide  (Al(OH),);  thus 


25.  CHEMICAL  AND   ELECTRICAL  METHODS.  Jl 

A1,(S04)S.K,S04  +  3H,0  +  3CaCO,  =  3CO,  +  3CaSO4 

+  KQSO.  +  2A1(OH).. 

Here  the  carbon  dioxide  is  a  gas,  the  calcium  and  potassium 
sulphates  remain  in  solution,  but  the  aluminum  hydroxide  is 
precipitated  in  the  form  of  a  flocculent  white  salt  which  in 
descending  clears  the  water  of  the  suspended  matter,  both 
organic  and  inorganic.  If  the  water  does  not  contain  calcium 
carbonate  there  must  be  added  sodium  carbonate  (Na,CO3), 
and  the  reaction  is  the  same  as  before,  Na  taking  the  place 
of  K,  while  the  aluminum  hydroxide  is  precipitated.  On 
account  of  the  cheapness  of  alum  it  is  extensively  used  in  the 
purification  both  of  water  and  sewage. 

.Iron  perchloride  (FeCl3)  and  •  sodium  carbonate  (Na,CO8) 
added  to  water  (HUO)  produce  carbon  dioxide  (CO2),  sodium 
chloride  (NaCl),  and  iron  hydroxide  (Fe(OH)3),  the  last  being 
a  substance  which  precipitates  and  clears  the  water.  This 
method  has  not  come  into  use. 

Potassium  permanganate  (K2Mn2O8)  added  to  water  gives 
a  purple  color,  and  if  used  in  sufficient  quantity  so  that  the 
color  persists  for  ten  minutes  it  causes  effective  purification. 
This  is  caused  partly  by  the  liberation  of  oxygen,  but  mainly 
by  the  formation  of  a  manganese  hydrate  which  is  precipi- 
tated. This  process  is  an  expensive  one  on  a  large  scale  and 
has  been  used  but  little.  A  solution  of  alum  and  potassium 
permanganate  has  been  recommended  to  be  used  by  soldiers 
to  purify  and  clarify  foul  water  which  is  found  near  their 
camps. 

Since  1910  the  use  of  a  disinfectant  in  purifying  water  has 
come  into  widespread  use,  especially  as  a  temporary  or  pre- 
cautionary measure.  The  most  important  and  widely  used  oi 
these  is  Hypochlorite  of  Lime,  known  also  as  Chloride  of  Lime 
or  Bleaching  Powder.  The  use  of  this  substance  was  first 
introduced  by  Dr.  Leal  at  Boonton,  N.  J.,  in  connection  with 
the  water  supply  for  Jersey  City  and  by  G.  A.  Johnson  at  the 


7  la  WATER  AND   ITS   PURIFICATION.  If; 

Union  Stock  Yards  in  Chicago.  The  results  obtained  by  its 
use  were  as  excellent  as  unexpected  and  its  adoption  has 
spread  rapidly  to  all  parts  of  the  world. 

The  composition  of  this  chemical  may  probably  be  ex- 
pressed by  the  formula  4CaOCl2,2Ca(OH)2,5H2O.  In  this, 
the  CaOCl2  is  the  calcium  hypochlorite  and  constitutes  about 
68  per  cent  of  the  whole.  The  other  two  ingredients  are  cal- 
cium hydroxide,  20  per  cent,  and  water,  12  per  cent.  The 
calcium  hypochlorite  forms  the  only  valuable  constituent,  the 
others  being  inert.  Hypochlorite  of  Lime  is  valued  according 
to  the  amount  of  ''available  chlorine,"  which  is  the  amount 
of  free  chlorine  derived  from  decomposing  the  hypochlorite 
with  acid.  Commercial  bleach  or  hypochlorite  usually  con- 
tains about  35  per  cent  available  chlorine. 

The  action  in  disinfecting  the  water  by  the  addition  of 
hypochlorite  is  oxidation  and  not  chlorination  as  is  often  sup- 
posed. The  extent  of  the  purification,  insofar  as  the  removal 
of  bacteria  is  considered,  is  remarkable,  more  than  90  per 
cent  reduction  being  the  rule  and  99  an,d  100  per  cent  being 
not  uncommon. 

The  amount  of  hypochlorite  used  varies  from  2  to  30  pounds 
per  million  gallons  of  water,  and  the  total  cost  usually  ranges 
from  15  to  25  cents  per  million  gallons  of  water  treated.  Its 
inexpensiveness,  together  with  its  high  efficiency  in  bacterial 
removal,  have  been  the  controlling  factors  in  its  widespread 
adoption.  While  it  is  used  in  many  places  as  a  permanent 
means  of  purifying  water,  both  alone  and  in  connection  with 
filtration  plants,-  its  use  has  doubtless  been  more  beneficial 
as  employed  by  many  municipalities  in  disinfecting  a  contam- 
inated water  supply  while  other  means  of  obtaining  a  pure 
water  were  being  prepared. 

The  use  of  hypochlorite  is  objected  to  by  many  on  account 
of  giving  the  water  a  bad  taste,  either  real  or  imagined.  If 


2$.  CHEMICAL   AND    ELECTRICAL    METHODS.  fib 

real,  it  has  been  due  to  improper  application,  for  when  prop- 
erly applied  no  tastes  or  odors  are  noticeable  when  the  water 
reaches  the  consumer.  Others  have  objected  to  it  on  the 
general  proposition  that  it  is  bad  policy  to  put  a  poison  into 
drinking  water.  While  many  lives  have  no  doubt  been  saved 
by  its  use  and  while  it  will  have  a  wide  field  of  usefulness  in 
the  future,  it  is  believed  that  the  present  tendency  is  too 
strong  toward  using  only  hypochlorite  and  neglecting  the  very 
valuable  filtration  processes  and  other  means  of  obtaining 
pure  water. 

Hypochlorite  of  sodium  has  also  been  used  to  some  extent, 
but  it  is  not  so  readily  obtainable  as  hypochlorite  of  calcium. 
It  can,  however,  be  very  inexpensively  made  and  will  doubt- 
less come  into  more  extended  use  in  the  future.  It  is  made 
by  passing  an  electric  current  through  a  solution  of  common 
salt  water.  The  effect  of  the  electric  current  is  to  liberate 
the  chlorine  (Cl)  in  the  salt  (NaCl)  and  this  with  the  oxygen 
in  the  water  forms  (NaOCl)  the  sodium  hypochlorite.  The 
action  in  disinfecting  is  the  same  as  in  the  use  of  calcium 
hypochlorite. 

Liquid  chlorine  has  been  used  to  a  limited  extent,  but  has 
not  come  into  general  use  on  account  of  its  expense.  Its 
action  is  the  same  as  the  hypochlorites  of  lime  and  sodium. 

Copper  sulphate  has  been  used  slightly  and  will  kill  some 
but  not  all  kinds  of  organisms.  It  is  more  particularly  used 
in  the  removal  of  odors  and  tastes  due  to  algae,  which  it  often 
seems  to  do  quite  effectively. 

The  so-called  electrical  methods  of  purification  are  really 
chemical  ones,  as  the  electric  action  merely  causes  chemical 
reactions  to  take  place.  One  of  these  is  the  decomposition 
of  some  of  the  water  into  oxygen  and  hydrogen,  with  the 
intention  of  furnishing  free  oxygen  to  act  upon  the  organic 
matter  like  the  oxygen  furnished  by  aeration.  In  fact,  how- 
ever, the  oxygen  generally  combines  with  the  iron  plates  at 


?2  WATER   AND    ITS    PURIFICATION.  II. 

the  positive  pole,  and  the  iron  oxide  thus  formed  is  precipi- 
tated and  clarifies  the  water.  This  method  can  be  employed 
only  on  a  small  scale,  and  its  use  is  very  limited.  When 
aluminum  plates  are  used  at  the  positive  pole  an  aluminum 
hydrate  is  precipitated. 

Ozone  has  been  tried  and  used  to  some  extent,  and  while 
it  has  been  successful  it  has  not  come  into  general  use  on 
account  of  the  expense.  Ozone  is  produced  by  discharging 
high  tension  electricity  through  air.  This  air  is  then  pumped 
through  the  water  or  the  water  is  allowed  to  fall  through  it. 
Ultra-violet  rays  have  also  been  used. 

Of  the  many  methods  of  disinfecting  water  none  has  come 
into  any  considerable  use  except  the  hypochlorite  treatment 
and  this  now  used  to  some  extent  by  probably  more  than 
one-half  of  the  urban  population  of  the  United  States.  Many 
devices  and  arrangements  have  been  designed,  and  many  of 
them  patented,  for  the  proper  mixing  and  applying  of  the 
hypochlorite  to  the  water. 

26.  SCREENS  AND  STRAINERS. 

All  household  filters  are  arranged  so  as  to  screen  or  strain 
the  water  as  it  passes  through  them.  A  fine  sieve  or  screen 
may  remove  most  of  the  suspended  matter,  but  the  dissolved 
matter  will  pass  through  it;  moreover,  after  a  few  days  of  use 
the  screen  becomes  so  clogged  with  the  suspended  matter 
that  some  of  this  may  be  dissolved  out  and  thus  render  the 
water  more  impure  than  before  the  operation.  All  household 
filters  hence  require  frequent  cleaning  in  order  to  maintain 
their  efficiency. 

Charcoal,  and  particularly  charcoal  made  from  the  bones  of 
animals,  is  one  of  the  most  effective  strainers.  It  is  formed 
into  plates,  and  these  are  arranged  in  a  box  so  that  all  the 
water  issuing  from  a  pipe  is  compelled  to  pass  through  them 
by  the  hydrostatic  pressure.  The  surfaces  of  the  plates,  and 


26.  SCREENS  AND  STRAINERS.  73 

their  interstices  also,  soon  become  clogged  with  organic 
matter,  and  it  is  necessary  to  take  them  out  and  remove  the 
organic  matter  by  heating  in  order  that  the  purification  of  the 
water  may  continue.  In  an  experiment  by  Frankland  it 
was  found  that  no  bacteria  appeared  in  the  filtered  water 
during  the  first  twelve  days  of  use  of  the  charcoal;  at  the  end 
of  a  month,  however,  the  filtered  water  contained  7000 
bacteria  per  cubic  centimeter,  which  was  five  times  as  many 
as  were  found  in  the  unfiltered  water.  In  general,  the  use  of 
these  charcoal  screens  is  a  source  of  danger  rather  than  a 
benefit. 

The  Pasteur  filter  consists  of  a  porcelain  cylinder  contained 
within  an  iron  tube  with  an  annular  space  between;  the  iron 
tube  is  connected  to  the  house-pipe  and  the  water  fills  the 
annular  space  and  is  forced  through  the  porcelain  under  the 
hydrostatic  pressure  when  the  faucet  is  open  which  connects 
with  the  inner  cylinder.  At  first  this  completely  removes  the 
bacteria,  but  later  they  are  sometimes  found  in  the  filtered 
water,  having  passed  through  the  porcelain  by  growth;  hence 
it  may  be  necessary  to  remove  the  porcelain  cylinder  once  a 
week  and  boil  it  for  half  an  hour  in  order  to  kill  the  bacteria 
that  it  contains.  The  Berkefeld  filter  is  similar  to  the  Pasteur 
filter,  but  the  straining  cylinder  is  of  diatomaceous  earth. 

On  a  large  scale,  sand,  coke,  and  sponges  have  been  used  as 
strainers,  these  being  arranged  in  beds  through  which  the  water 
passes,  but  the  beds  require  to  be  renewed  or  cleaned  at 
regular  intervals. 

Spongy  iron,  made  by  blowing  air  through  iron  ore  in  a 
highly  heated  state,  is  a  porous  material  which  has  been 
much  used  in  Europe.  It  may  act  as  a  strainer,  but  its  true 
action  is  that  of  causing  precipitation,  which  it  does  by  the 
production  of  a  ferric  hydroxide  under  the  action  of  the  free 
oxygen  in  the  water. 

It  is  seen  that  these  screens  and  strainers  do  not  use  the 


WATER  AND   ITS   PURIFICATION.  II. 

/e  of  purifying  water  by  natural  filtration  which  has 
been  Explained  in  Art.  23,  as  that  method  removes  the 
organic  matter  through  a  slow  process  under  the  action  of 
bacteria  and  oxygen.  Although  popularly  called  filters,  they 
are  so  only  in  the  sense  of  sieves  or  strainers,  and  the  prin- 
ciple of  their  action  should  not  be  confounded  with  that  of 
true  filtration. 

27.      MECHANICAL   FILTERS. 

The  general  principle  of  all  mechanical  filters  is  the  same, 
namely,  rapid  straining  of  water  through  sand  which  is 
cleaned  at  frequent  intervals.  The  method  of  operation  of  a 
mechanical  filter  may  be  briefly  described  as  follows :  a  tank 
contains  at  the  bottom  a  strainer  system  of  perforated  pipes 
or  brass  plates  which  supports  a  quantity  of  gravel  and  sand. 
Most  filters  have  10  or  12  inches  of  gravel  on  which  is  placed 
about  30  inches  of  sand.  The  purpose  of  the  gravel  is  merely 
to  support  the  sand  and  keep  it  out  of  the  strainer  system;  it 
has  no  function  in  the  filtration  process  itself.  The  water  to 
be  filtered  enters  at  the  top  and  is  distributed  over  the  sand, 
through  which  it  filters  at  a  rapid  rate,  is  caught  by  the  strainer 
system  and  conveyed  to  a  filtered  water  reservoir,  usually 
located  beneath  the  filter.  From  this  the  water  is  delivered 
to  the  street  mains  either  by  gravity  or  by  pumping,  if  this  is 
required.  The  filter  is  frequently  washed,  at  intervals  varying 
from  8  to  48  hours,  depending  on  the  impurity  of  the  water, 
by  reversing  the  direction  of  flow  and  having  it  pass  upward 
through  the  sand,  thereby  carrying  off  the  dirt  from  the  sur- 
face. This  dirty  water  is  conveyed  by  pipes  to  the  sewer. 
The  water  used  for  washing  is  filtered  water,  about  3  per  cent 
of  the  capacity  of  the  plant  being  required  for  this  purpose. 
The  rate  of  mechanical  filters  is  usually  about  3000  gallons 
per  square  foot  of  filter  surface  per  day. 


27-  MECHANICAL   FILTERS.  75 

In  the  first  mechanical  filters  the  sand  was  agitated  by  a 
rake  during  the  washing  and  this  idea  is  still  used  in  some  of 
the  small  household  plants.  Compressed  air  has  also  been 
used  to  a  considerable  extent,  this  being  introduced  at  the 
bottom  of  the  sand  at  the  same  time  as  the  wash  water  or 
immediately  preceding  it.  When  air  is  not  used  a  higher 
velocity  is  required  in  the  wash  water  to  properly  cleanse  the 
filter. 


JEWELL  MECHANICAL  FILTER. 

The  above  figure,  furnished  by  the  New  York  Continental 
Jewell  Filtration  Co.,  shows  one  of  the  smaller  types  of  me- 
chanical filter,  known  as  the  Jewell  filter.  This,  and  similar, 
types  are  often  used  by  isolated  institutions,  hotels,  etc.,  and 
usually  operate  under  pressure.  Larger  ready-built  filters  are 
also  made  having  capacities  as  high  as  600000  gallons  in  24 
hours.  The  larger  type  all  operate  under  pressure  and  do  not 
have  the  rake  for  stirring  the  sand,  but  are  cleansed  by  having 
a  much  higher  velocity  to  the  wash  water.  The  operation  01 
this  filter  is  well  shown  by  the  figure  and  needs  no  further 
explanation. 


76 


WATER   AND    ITS    PURIFICATION. 


II, 


The  type  of  mechanical  filter  usually  built  for  municipal 
supplies  is  constructed  of  concrete  tanks  and  an  elaborate 
system  of  piping.  The  general  arrangement  is  as  shown  in 
the  figure.  No  two  filter  plants  of  this  type  are  exactly  alike, 


Effluent  Effluent 

SECTION  THROUGH  MECHANICAL  FILTER  AND  PIPE  GALLERY. 

the  requirements,  the  local  conditions  and  the  opinions  of  the 
designer  creating  marked  differences,  but  the  general  principle 
involved  is  the  same  in  them  all.  The  water  enters  the  filter 
through  the  pipe  marked  influent,  whence  it  flows  through  a 
central  gutter  between  two  sand  beds.  It  then  rises  and  over- 
flows the  gutter  onto  the  sand  beds,  the  head  being  sufficient 
to  make  it  stand  from  two  to  three  feet  above  the  level  of  the 
sand.  After  percolating  through  the  filter  it  is  collected  under 
the  strainer  system  and  conveyed  by  gravity  to  the  effluent 
pipes  from  which  it  is  carried  into  the  filtered  water  reservoir, 
usually  located  beneath  the  filters.  A  "rate  controller"  is  in- 
serted in  the  effluent  pipe  at  each  filter  unit.  This  is  an 
arrangement  of  valves  which  automatically  increases  or  de- 
creases the  rate  of  filtration  as  the  loss  of  head  due  to  the 
clogging  of  the  filter  is  increased  or  decreased. 

When  it  becomes  necessary  to  wash  this  filter,  the  valves 


2?.  MECHANICAL   FILTERS.  760, 

marked  i  and  2  are  closed  and  those  marked  3  and  4  are 
opened.  The  wash  water,  which  is  under  a  considerable  head, 
then  passes  upward  through  the  strainer  system  and  the  sand 
and  washes  the  dirt  and  impurities  from  the  surface.  This 
dirty  water  is  caught  by  the  lateral  wash  water  gutters  and 
conveyed  to  the  drain.  The  process  of  washing  requires  from 
10  to  15  minutes.  After  the  filter  has  been  washed,  the  valves 
3  and  4  are  closed,  I  and  2  are  opened  and  the  filter  begins 
operations  again.  Arrangement  is  usually  made  to  waste  the 
first  few  minutes  run  of  the  filter  after  it  has  been  washed 
until  the  sand  bed  becomes  covered  with  the  coating  which  is 
essential  to  the  proper  filtering  of  the  water.  The  velocity  of 
the  wash  water  must  not  be  so  high  as  to  carry  particles  of 
the  sand  into  the  wash  troughs.  All  of  the  valves  for  one 
filter  unit  are  usually  operated  from  a  central  control,  located 
on  the  operating  floor.  They  are  operated  either  by  hydraulic 
or  electric  methods. 

Plants  of  this  type  always  contain  more  than  one  filter  unit, 
in  order  that,  during  washing,  cleaning  or  repairing,  and  to 
provide  for  future  demands  and  contingencies,  there  may  be 
no  interruption  in  the  service.  The  number  of  beds  or  units 
in  a  plant  varies  from  6  in  the  smallest  to  40  in  the  largest 
plant,  recently  constructed  at  St.  Louis,  Mo. 

In  nearly  all  mechanical  filter  plants  the  water  is  first  treated 
with  chemicals  as  explained  in  Art.  25.  This  removes  much 
of  the  suspended  and  organic  matter  and  relieves  the  filter  of 
a  considerable  part  of  its  burden,  as  well  as  increasing  the 
periods  between  washings.  A  disinfectant,  such  as  hypo- 
chlorite  of  lime,  is  also  often  added,  sometimes  before  and 
sometimes  after  filtration. 

The  following  analyses  show  the  effects  of  the  purification 
of  the  water  of  the  Passaic  River  at  Little  Falls,  N.  J.,  by 
the  mechanical  plant  described  in  Art.  84.  The  figures, 
which  are  in  parts  per  million,  are  the  averages  of  four  analyses 


WATER  AND  ITS  PURIFICATION.  II. 

made   in   October  and    November,  1902,  the  samples  being 

taken   weekly.      The   filtration   rendered   the  slightly   turbid 
river  water  clear  and  colorless. 

Before.  After. 

Hardness,  25  23 

Total  Solids,  73  68 

Chlorine,  3.3  3.2 

Albuminoid  Ammonia,  0.206  0.122 

Free  Ammonia,  0.030  0.020 

Nitrogen  as  Nitrates,  0.026  0.093 

Nitrogen  as  Nitrites,  0.003  o.ooo 

Oxygen  consumed,  7.8  1.8 

Bacteria,  per  cubic  centimeter,  3700  81 

The  success  of  mechanical  filters  as  a  means  of  purifying 
water  is  well  shown  by  the  fact  that  during  the  past  twenty 
years  there  have  been  built  over  300  plants  of  this  type  in  the 
United  States  alone.  The  largest  of  these,  with  their  capac- 
ities in  millions  of  gallons  per  day,  are  shown  in  the  table 
feelow : 

St.  Louis,  Mo 160 

Baltimore,  Md 128 

Cincinnati,  0 112 

New  Orleans,  La 44 

Louisville,  Ky 37 

Little  Falls,  N.  J.  (East  Jersey  Water  Co.) 32 

Columbus,  O ,....' 30 

Minneapolis,  Minn 29 

Hackensack,  N.  J.  (Hackensack  Water  Co.) 24 

Atlanta,  Ga 21 

Toledo,  0 20 

Grand  Rapids,  Mich 20 

In  addition  to  these  there  are  in  operation  in  the  United 
States  thousands  of  house  filters,  such  as  that  shown  in  this 
article,  and  filtering  from  several  hundred  to  several  thousand 
gallons  per  day,  all  of  which  employ  the  principles  of  mechan- 
ical filtration. 


28.  SLOW    SAND    FILTRATION.  77 

There  can  be  no  doubt  but  that  the  mechanical  sand  filters 
are  able  to  purify  all  but  the  most  incorrigible  waters  if  the 
cleaning  be  carried  on  at  intervals  sufficiently  frequent.  The 
construction  and  operation  of  such  a  mechanical  plant  is  a 
matter  that  involves  considerable  expense  to  a  town,  but  the 
same  must  be  said  regarding  the  system  of  artificial  filtration 
by  sand-beds  which  is  to  be  described  in  the  following  articles. 
Which  of  these  should  be  selected  for  the  treatment  of  an 
unsatisfactory  supply  can  only  be  decided  after  a  comparison 
of  plans  prepared  by  an  experienced  engineer. 


23.    SLOW  SAND  FILTRATION. 

Slow  sand  filtration  is  an  imitation  of  the  process  of  natural 
filtration  which  is  described  in  Art.  23.  Beds  of  sand  and 
gravel  are  prepared  on  the  ground,  and  the  water  is  allowed  to 
pass  through  them  at  a  slow  rate,  so  as  to  afford  sufficient 
time  for  the  useful  bacteria  to  decompose  the  organic  matter 
into  harmless  constituents.  The  purified  water,  often  called 
the  effluent  or  the  filtrate,  runs  out  at  the  bottom  of  the  beds 
and  is  collected  in  basins  for  distribution.  In  this  manner  an 
impure  surface  water  is  turned  into  a  pure  ground  water,  the 
organic  matter  and  ammonias  being  decreased,  the  chlorine 
remaining  constant,  and  the  inorganic  matter  and  nitrates 
being  increased. 

The  following  figure  shows  a  diagrammatic  section  of  a 
slow-sand  bed.  At  the  top  there  is  from  3  to  4  feet  of  fine 
sand,  below  this  there  is  from  i  to  2  feet  of  graded  gravel  or 
broken  stone  overlaid  with  gravel.  After  passing  through  the 
sand  and  gravel  the  water  is  collected  by  drains,  placed  in  the 
bottom  of  the  bed,  and  led  to  a  basin,  from  which  it  is  pumped 
or  delivered  by  gravity  to  the  town.  The  filter  bed  has  a 
concrete  bottom,  in  order  to  prevent  the  inflow  of  ground 
water  and  to  insure  that  the  effluent  shall  pass  into  the  drains 


WATER   AND    ITS    PURIFICATION. 


II. 


or  collectors.     Filters  are  usually  covered  with  masonry  roofs 
to  prevent  the  action  of  frost  on  the  filter  bed. 


SAND  FILTER  BED. 


When  this  method  is  to  be  applied  to  a  river  water  it  is 
first  pumped  to  a  reservoir  which  affords  opportunity  for 
sedimentation.  In  the  passage  from  the  reservoir  to  the 
filter  bed  it  is  well  also  to  cause  aeration  in  order  to  furnish 
oxygen  to  the  bacteria.  The  proper  rate  of  flow  through  the 
bed  is  insured  by  regulating  the  height  of  the  water  level  over 
the  beds  or  in  the  receiving  basin  so  that  the  head  may  be 
sufficient  to  cause  that  flow.  Different  kinds  of  water  require 
different  rates  of  filtration;  common  river  water  needs  about 
one  square  foot  of  filter-bed  surface  for  each  60  gallons  of 
water  filtered  in  one  day,  or  the  rate  of  filtration  is  60  gallons 
per  square  foot  of  surface  per  day.  A  very  impure  river 
water  may,  however,  weed  a  rate  as  low  as  30  gallons  per 
square  foot  of  surface  per  day,  while  a  lake  water  may  be 
filtered  at  a  rate  as  high  as  100  gallons  per  square  foot  of  sur- 
face per  day.  The  more  impure  the  water  the  lower  must  be 
the  rate  of  filtration,  as  more  time  is  required  for  the  bacteria 
to  decompose  and  nitrify  the  organic  matter, 


28.  SLOW    SAND    FILTRATION.  79 

The  depths  of  the  different  layers  of  the  filter  bed  and  the 
relative  proportions  of  sand  and  gravel  used  are  subject  to 
much  variation  in  constructions  by  different  engineers.  It 
is,  however,  universally  agreed  that  the  upper  sand  layer  is 
the  most  important,  since  the  activity  of  the  bacteria  is  the 
greatest  near  the  surface,  where  fresh  air  is  always  present. 
It  is  for  this  reason  that  the  rate  of  filtration  is  practically 
independent  of  the  depth  of  the  filter  bed.  One  foot  of  fine 
sand  in  the  upper  layer  is  probably  as  efficient  as  two  feet, 
but  owing  to  the  diminution  in  depth  caused  by  cleaning  the 
original  depth  of  this  should  be  greater  than  one  foot.  The 
intermediate  gravel  layer  acts  merely  as  a  support  to  the 
sand,  while  the  stone  layer  serves  to  distribute  the  water  to 
the  underdrains  which  are  laid  at  intervals  through  it. 

This  method  of  slow  sand  filtration  was  developed  in  Europe 
about  1860  as  a  result  of  the  study  of  natural  filtration.  It  is 
now  extensively  used  there,  and  furnishes  purified  water  to 
more  than  20  ooo  ooo  people.  In  Art.  9  one  of  the  instances 
is  given  where  the  use  of  such  filter  beds  prevented  the 
spread  of  cholera,  and  everywhere  it  has  been  found  that  the 
rate  of  deaths  from  typhoid  fever  has  been  materially 
decreased.  In  the  United  States  the  method  was  first  used  at 
Poughkeepsie,  N.  Y.,  in  1872;  a  plant  was  built  at  Hudson, 
N.  Y.,  in  1888,  and  one  at  Nantucket,  Mass.,  in  1892.  The 
beds  constructed  in  1893  by  Mills  at  Lawrence,  Mass.,  attracted 
wide  attention  to  this  method  of  filtration,  for  the  typhoid 
death  rate  was  reduced  nearly  one-half  in  the  first  year  of  its 
operation.  The  first  plant  for  treating  the  supply  of  a  large 
city  was  that  built  by  Hazen  in  1899  at  Albany,  N.  Y. 
Many  plants  have  since  been  constructed,  those  at  Philadelphia 
and  Pittsburg  being  the  largest. 

The  following  analyses  of  the  water  from  the  Merrimac 
River,  and  of  the  same  water  after  passing  through  the 
Lawrence  filter  beds,  will  give  an  idea  of  the  results  accom- 
plished by  artificial  filtration ;  the  figures  are  the  averages  of 


80  WATER   AND    ITS    PURIFICATION.  II. 

daily  analyses  made  by  the  Massachusetts   State  Board  of 
Health  during  the  month  of  July,   1895  : 

River.  Effluent.  Reservoir. 

Hardness,  parts  per  million   18  24  24 

Chlorine,  "  "        2.7  3.9  2.8 

Free  Ammonia,  "        0.134  0.075  0.022 

Albumenoid  Ammonia, "  "        0.243  0.097  0.099 

Nitrogen  as  Nitrates,     "  "        o.no  0.450  0.450 

Nitrogen  as  Nitrites,  0.003  o.ooi  o.ooi 

Oxygen  consumed,  "        3.8  2.4  2.1 

Bacteria  per  cubic  centimeter,  10000  50  69 

Here  the  purification  of  the  effluent  is  shown  by  the 
decrease  in  the  ammonias  and  nitrites  and  by  the  increase  in 
nitrates,  but  particularly  by  the  decrease  in  the  number  of 
bacteria.  The  effect  on  the  effluent  by  subsequent  sedimen- 
tation in  the  distributing  reservoir  is  mostly  apparent  in  the 
decrease  of  free  ammonia  and  oxygen  consumed,  but  the  July 
heat  caused  a  slight  increase  in  the  number  of  bacteria. 

Several  plants  have  been  constructed  in  this  country  in 
which  the  water  is  filtered  through  mechanical  filters,  as 
described  in  Art.  27,  prior  to  filtering  through  the  slow-sand 
beds.  This  method  is  called  double  filtration.  Examples  of 
this  type  of  plant  are  found  at  Philadelphia  and  at  Montreal. 

29.  OPERATION  OF  FILTER  BEDS. 

The  size  of  a  filter  area  depends  upon  the  quantity  of  water 
to  be  filtered  and  the  rate  of  filtration.  For  a  town  of  25  ooo 
inhabitants,  using  100  gallons  per  person  per  day,  the  average 
consumption  will  be  2  500  ooo  gallons  per  day,  and  at  a  rate 
of  filtration  of  60  gallons  per  square  foot  of  surface  per  day 
about  42  ooo  square  feet,  or  nearly  one  acre,  of  ground  is 
required.  Owing  to  the  cleaning  of  the  surface,  which  is 
periodically  necessary,  and  owing  to  the  fact  that  the  maxi- 
mum consumption  may  be  much  greater  than  the  mean,  it  is 


2Q.  OPERATION    OF   FILTER    BEDS.  8 1 

well  to  provide  a  larger  area,  say  if  or  2  acres.  This  may 
be  divided  into  three  or  four  beds,  so  that  one  may  be  thrown 
out  of  use  when  it  becomes  necessary  to  clean  its  surface. 

Each  bed  is  separated  from  the  others  by  walls  and  its 
bottom  is  water-tight.  A  series  of  drains  with  loose  joints  is 
laid  on  the  bottom,  and  these  are  connected  with  one  or  two 
main  drains  which  discharge  the  effluent.  Arrangement  must 
be  made  to  waste  the  effluent  instead  of  allowing  it  to  run  to 
the  settling  basin,  as  this  is  necessary  for  a  day  or  two  after 
starting  the  filtration ;  also  means  for  draining  the  bed  when 
it  is  to  be  put  out  of  use  must,  be  provided.  The  stone, 
gravel,  and  fine  sand  are  then  applied  in  successive  layers, 
great  care  being  exercised  that  at  the  same  depth  below  the 
surface  the  distribution  should  be  uniform  over  the  entire  area 
of  the  bed.  The  sand  in  the  upper  layer  should  be  so  fine 
that  ten  per  cent  of  it  has  grains  whose  diameter  is  between 
0.2  and  0.4  millimeters. 

When  the  water  is  admitted  upon  the  filter  bed  the  rate  of 
flow  will  be  greater  for  the  same  head  than  after  it  has  been 
in  operation  for  a  few  days.  This  retardation  is  due  to  the 
collection  of  organic  matter  in  the  top  of  the  sand,  forming  a 
so-called  dirt  layer,  from  one-half  an  inch  to  one  inch  in 
thickness,  and  it  is  found  that  effective  purification  does  not 
occur  until  this  has  been  formed.  Hence  for  the  first  day  or 
two  it  is  best  to  waste  the  effluent  instead  of  collecting  it. 
This  dirt  layer  should  not  be  broken,  for  if  so  the  water  that 
'passes  through  the  holes  is  ineffectively  purified.  As  the  dirt 
layer  becomes  thicker  and  thicker  the  flow  becomes  more  and 
more  impeded,  so  that  finally,  after  an  operation  of  from  two 
to  six  weeks,  it  is  found  necessary  to  drain  the  bed  and  clean 
its  surface. 

The  cleaning  is  accomplished  by  removing  that  part  of  the 
sand  which  contains  the  dirt  layer,  the  thickness  of  this  being 
usually  about  one  inch.  The  filter  bed  is  then  put  into 


82  WATER   AND    ITS    PURIFICATION.  II. 

operation  again  until  a  second  cleaning  is  necessary.  After 
several  inches  of  sand  have  been  removed  fresh  sand  is 
applied  to  restore  the  thickness,  the  dirty  sand  being  gen- 
erally washed  for  this  purpose. 

The  great  importance  of  the  dirt  layer  will  be  better  appre- 
ciated when  it  is  stated  that  it  contains  more  than  one-half  of 
the  total  number  of  bacteria  in  the  filter  bed;  at  a  depth  of 
one-quarter  inch  below  the  surface  the  number  of  bacteria  is 
about  ten  times  as  great  as  at  a  depth  of  one  inch,  and  at  a 
depth  of  two  inches  the  number  is  only  about  one-fourth  of 
that  at  a  depth  of  one  inch.  These  bacteria  are  doing  the 
useful  work  of  decomposing  the  organic  matter  of  the  water 
by  permitting  the  oxygen  to  cause  its  combustion  and  nitrifi- 
cation. 

The  method  above  described  is.called  continuous  filtration, 
as  the  head  of  water  remains  constant  in  the  interval  between 
the  cleanings.  Another  method,  which  is  less  often  used,  is 
that  called  intermittent  filtration;  in  this  the  bed  is  drained 
from  time  to  time,  in  order  to  allow  the  air  to  enter  and  thus 
furnish  oxygen  to  the  bacteria.  The  filter  beds  at  Lawrence, 
Mass.,  are  of  this  type,  they  being  drained  once  a  day  to 
secure  aeration,  and  the  cleaning,  when  necessary,  is  done 
during  the  periods  of  daily  rest. 

In  the  latest  filters  a  machine  for  washing  the  sand  is  run 
on  rails  above  the  filter.  This  machine  picks  up  the  sand 
from  the  bed,  washes  it,  and  returns  it  to  the  bed.  The  dirty 
water  is  conveyed  by  a  flexible  pipe  to  the  drain  located  ad- 
jacent to  the  bed. 

Most  filter  beds  are  covered  with  masonry  vaults  to  pro- 
tect them  from  the  action  of  frost,  as  this  impedes  the  activity 
of  the  bacteria  and  hence  lessens  the  efficiency  of  the  purifica- 
tion. The  cleaning  of  an  open  filter  cannot  be  well  done  in 
freezing  weather,  while  that  of  a  covered  one  is  done  as  effect- 
ively in  winter  as  in  summer. 


29.  OPERATION   OF  FILTER   BEDS.  83 

The  cost  of  construction  and  maintenance  of  a  filter-bed 
system  constitutes  a  material  addition  to  the  usual  expenses 
of  operating  a  water-supply  system.  An  estimate  by  Hazen 
for  a  city  using  10  ooo  ooo  gallons  per  day  and  having  an  area 
of  five  acres  for  the  filter  beds  gives  $350000  for  the  cost  of 
construction  if  the  beds  are  to  be  vaulted,  and  about  $43  per 
day  as  the  cost  of  operation.  Taking  into  account  the 
interest  on  the  cost  of  construction  and  the  sinking-fund 
contribution  necessary  to  repay  the  same,  the  total  cost  of 
filtration  may  be  put  at  ij  cents  per  thousand  gallons,  or 
about  46  cents  per  person  per  year,  if  the  average  consump- 
tion be  reckoned  at  100  gallons  per  day.  But  this  expense 
must  be  met  when  a  city  is  using  a  water  so  impure  as  to  raise 
the  typhoid  death  rate  above  the  normal  for  the  surrounding 
region. 

In  conclusion  it  may  be  said  that  although  artificial  filtra- 
tion is  an  imitation  of  the  process  of  natural  filtration,  it  differs 
from  it  in  one  particular.  In  nature  the  process  of  purifying 
surface  water  is  materially  aided  by  the  vegetation  growing 
on  the  surface,  as  this  absorbs  not  only  the  most  impure  water 
but  also  the  products  of  nitrification.  In  artificial  filtration 
the  office  of  vegetation  is  replaced  by  the  process  of  cleaning 
the  filter  beds,  and  the  manner  in  which  this  is  done  is  most 
important.  In  fact,  to  secure  the  best  results  it  is  indispen- 
sable that  regular  bacteriological  examinations  of  the  unfiltered 
water  and  of  the  effluent  should  be  made,  in  order  that  the 
effect  of  the  methods  of  operating  and  cleaning  the  beds  may 
be  definitely  known,  and  that  warnings  may  be  given  of  ?ny 
imperfections.  In  Germany  such  bacteriological  analyses  are 
required  to  be  made  daily.  Frequent  chemical  analyses  are 
also  of  value  to  supplement  and  verify  the  conclusions  of  th« 
bacteriological  ones,  and  detailed  records  of  the  rate  of  filtra- 
tion must  be  kept.  Thus  by  well-laid  plans  and  eternal  vigil- 
ance in  executing  them  the  sanitary  engineer  transforms  the 
water  of  a  foul  river  into  a  safe  public  supply. 


84  WATER  AND   ITS   PURIFICATION.  II. 


30.  EXERCISES  AND  PROBLEMS. 

16  (a)  Consult  Report  of  United  States  Weather  Bureau  for  1891- 
92,  page  32,  and  describe  the  Eccard  self-recording  rain  and  snow 
gage. 

16  (b)  Consult   Science  for  December  2,   1892,  and  state  views 
regarding  the  influence  of  the  moon  on  the  rainfall. 

17  (a)  Consult   Fitzgerald's  article  in  Transactions  of  American 
Society  of  Civil  Engineers  for  1886,  and  describe  his  self-recording 
evaporometer. 

17  (b)  Consult  Rafter's  Hydrology  of  the  State  of  N^w  York 
(Albany,  1905),  or  Merriman's  Treatise  on  Hydraulics  (New  York* 
1916),  and  obtain  a  synopsis  of  Vermeule's  conclusions  regarding  the 
relation  of  evaporation  to  rainfall  and  temperature. 

18.  Consult  Mason's  Water  Supply  (New  York,  1896),  and  inter- 
pret the  chemical  analyses  of  city  and  country  snow  on  page  213. 

19.  Consult  Report  of  State  Board  of  Health  of  Massachusetts 
for   1891,  and  describe  more  fully  the  investigations  of  Drown  on 
the  semi-annual  turnover  of  the  water  in  deep  ponds  and  reser- 
voirs. 

20  (a)  Consult  the  same  report  for  1892,  pages  715-725,  and  de- 
scribe how  a  typhoid  fever  epidemic  in  Springfield,  Mass.,  was 
caused  by  milk  which  had  been  infected  from  a  polluted  well. 

20  (b)  What  is  the  derivation  of  the  word  Artesian  ?     Describe 
the  artesian  well  at  Crenelle,  France;  also  those   of  Terre  Haute, 
Ind.,  Columbus,  O.,  and  Chicago,  111. 

21  (a)  Read   the   description   of   Lake   Mceris   given   by   Herodotus, 
What  methods  did  Hippocrates  advise  for  the  purificatipn  of  drink- 
ing water? 

21  (6)  Consult  Transactions  American  Society  of  Civil  Engineers  for 
1914  and  ascertain  facts  regarding  a  reinforced  concrete  reservoir  at  St. 
Louis,  Mo. 

22  (a)  An  approximate  formula  for  the  velocity  of  fall  of  a  smooth 
spherical  body  in  water  is  v  =  V  2gd(s  —  i),  in  which  g  is  the  ac- 
celeration of  gravity,  d  the  diameter  of  the  body,  and  5  its  specific 
gravity.     Compute  the  time  required  for  a  particle  having  a  diameter 
of  o.o  i  inch  and  a  specific  gravity  of  1.8  to  fall  in  a  reservoir  through 
a  height  of  16  feet. 


30.  EXERCISES    AND    PROBLEMS.  85 

22  (b)  Consult  Engineering  Record,  August  13,  1898,  and  give 
facts  regarding  the  reduction  of  number  of  bacteria  by  sedimenta- 
tion. 

23.  Consult  Report  on  Water  Supply  and  Sewerage  of  Massachu- 
setts State  Board  of  Health  (Boston,  1890),  and  give  descriptions 
of  filter  galleries  and  basins  at  Framingham,  Newton,  Waltham,  and 
Wellesley. 

24  (a)  One  of  the  seven  articles  that  a  Buddhist  monk  is  allowed 
to  possess  is  a  sieve.  What  use  does  he  make  of  it,  and  why  ? 

24  (b)   Explain  what  occurs  when  sodium  carbonate  (Nn.,CO3)  is 
added  to  water  containing  calcium  sulphate   (CaSO4)   in  solution. 

25  (a)  If    100    pounds    of    commercial    alum   (Al2(SO4)3.KaSO4. 
24HaO)  be  dissolved  in  water,  show  that  the  weight  of  the  precipi- 
tate is  about  1 6  pounds. 

27.  Consult  Stein's  Water  Purification  Plants  and  their  Operation 
(New  York,  1915)  and  obtain  sketches  of  the  mechanical  filter  plant  at 
Minneapolis,  Minn. 

28  (a)  Consult  Transactions  of  American  Society  of  Civil  Engineers 
for  June,  1911,  and  compare  results  of  operation  of  the  Washington, 
D.  C.,  niters  during  the  summer  and  winter  months. 

28  (6)  Consult  Hazen's  Filtration  of  Public  Water  Supplies  (New 
York,  1896),  and  describe  how  the  efficiency  of  filtration  depends  upon 
the  size  of  the  sand  grains  in  the  upper  layer  of  the  filter  bed. 

28  (c)  Consult  Engineering  News,  March  9,  1911,  and  give  a  descrip- 
tion of  the  Toronto  slow  sand  filtration  plant. 

29  Consult  the  engineering  journals  and  obtain  a  description  of  the 
vaulted  filter  beds  built  in  1889  at  Albany,  N.  Y.,  or  of  those  built  from 
1902  to  1906  at  Philadelphia,  Pa. 

30  (a)  Consult  engineering  journals  for  January,  1907,  and  find  the 
recommendations  made  by  Hazen  and  Fuller  regarding  stripping  the  site 
of  the  great  Ashokan  reservoir  of  the  Catskill  water  supply  of  New 
York  City. 

30  (b)  Consult  Canadian  Engineer,  Jan.  18,  1912,  and  determine 
facts  regarding  the  works  of  the  Montreal  double  filtration  plant. 


86  WATER-SUPPLY  SYSTEMS.  III. 


CHAPTER  III. 
WATER-SUPPLY   SYSTEMS. 

31.  CLASSIFICATION. 

Water-supply  systems  may  be  divided  into  two  classes: 
gravity  systems  and  pumping  systems.  A  gravity  system  is 
one  that  collects  the  water  of  brooks  in  a  reservoir  and  dis- 
tributes it  by  gravity.  A  pumping  system  is  one  that  elevates 
the  water  of  a  river  or  lake  by  means  of  pumps.  The  term 
"  water- works"  applies  to  both  systems,  and  means  a  com- 
plete plant  for  the  collection  and  distribution  of  a  public 
supply. 

The  simplest  gravity  system  has  but  one  reservoir,  which 
serves  both  to  collect  the  water  and  to  distribute  it  to  the 
town.  A  more  complete  gravity  system  is  that  which  has 
two  kinds  of  reservoirs,  one  to  collect  and  store  the  water, 
and  the  other  for  its  distribution.  The  term  storage  system 
is  also  frequently  used  instead  of  gravity  system  for  this  class 
of  water-works.  Sometimes  a  town  may  have  two  or  more 
distributing  reservoirs  for  the  supply  of  different  sections,  all 
being  fed  from  the  same  storage  reservoir.  Sometimes  a 
town  may  have  two  or  more  storage  reservoirs  which  collect 
water  from  different  brooks.  In  general,  one  collecting  reser- 
voir, with  its  distributing  reservoirs  and  the  pipes  that  lead 
from  them,  is  called  a  gravity  water- works. 

Pumping  systems  are  divided  into  two  classes  according  to 
the  method  in  which  the  water  is  distributed.  The  first  class 
is  where  water  is  pumped  to  a  reservoir  from  which  it  flows 


31.  CLASSIFICATION.  87 

by  gravity  to  the  town;  the  second  class  is  where  the  water 
is  pumped  directly  into  the  main  pipe  leading  to  the  town. 
In  the  first  class  opportunity  is  afforded  for  aeration  and 
sedimentation,  and  the  reservoir  contains  a  supply  for  several 
days,  so  that  the  pump  may  be  stopped  when  the  river  water 
is  turbid.  In  the  second  class  tanks  and  stand-pipes  are 
sometimes  provided,  but  these  hold  a  small  supply  and  there 
is  little  opportunity  for  sedimentation,  since  most  of  the  water 
goes  directly  to  the  houses;  accordingly,  the  water  delivered 
by  this  method  should  be  of  very  pure  quality  before  it  passes 
to  the  pumps. 

The  first  public  water  supply  in  the  United  States  was  at 
Boston,  Mass.,  where  in  1652  a  reservoir  12  feet  square  was 
constructed,  to  which  water  was  brought  through  wooden 
pipes  from  neighboring  springs.  Nothing  further  appears  to 
have  been  done  until  1795,  when  the  supply  was  increased 
and  wooden  pipes  were  laid  for  its  distribution. 

The  second  public  water  supply  in  the  United  States  was 
at  Bethlehem,  Pa.,  where  in  1754  a  millwright  named  Hans 
Christopher  Christiansen  built  a  wooden  pump  which  forced 
the  water  of  a  spring  through  a  line  of  pitch-pine  pipes 
680  feet  long  to  a  wooden  reservoir  70  feet  above  the  spring, 
the  pump  being  operated  by  an  undershot  wheel  in  a  neigh- 
boring creek.  In  1762  the  wooden  pump  was  replaced  by 
three  cast-iron  pumps  of  4  inches  diameter  and  18  inches 
stroke,  gum-wood  pipes  used  instead  of  pitch-pine,  the  height 
of  lift  increased  to  1 12  feet,  and  from  the  reservoir  pipes  were 
laid  to  distribute  the  water  to  tanks  and  cisterns  in  the 
vicinity  of  the  principal  dwellings.  The  cost  of  this  system, 
including  the  pump  house,  was  £514  i6s.  $d. 

Prior  to  1800  there  were  built  in  the  United  States  of 
America  only  five  public  water-works,  and  prior  to  1851  only 
68.  From  1851  to  1860  there  were  built  61,  while  from 
1 86 1  to  1870  the  number  was  104.  After  1870  the  number 


88  WATER-SUPPLY    SYSTEMS.  III. 

annually  constructed  increased  with  great  rapidity,  so  that  in 
1880  there  were  629  in  "operation. 

In  the  Manual  of  American  Water-Works  for  1888  there 
are  described  1598  water- works  and  in  1897  there  are  recorded 
3196  water- works  furnishing  both  domestic  supply  and  fire 
protection  to  3480  towns,  and  also  462  furnishing  a  partial 
supply.  In  1915  there  were  probably,  at  least,  6000  towns  in 
the  United  States  which  had  water-works. 

The  sources  of  supply  of  these  water-works  embrace  all  the 
different  kinds  of  surface  and  ground  waters  described  in  the 
la-t  chapter.  The  relative  proportions,  as  inferred  from 
FJynn's  analysis  of  the  records  for  1897,  are  about  as  follows: 
40  per  cent  of  the  water-works  use  surface  waters  and  60  per 
cent  ground  waters;  of  the  40  per  cent  of  surface  waters  about 
6  per  cent  are  from  brooks  and  creeks,  27  per  cent  from 
rivers,  and  7  per  cent  from  lakes;  of  the  60  per  cent  of  ground 
waters  about  18  are  from  springs  and  42  from  wells. 

The  extent  to  which  the  different  systems  are  used  is  also 
given  roughly  by  the  following  figures  for  1897:  of  gravity 
systems  there  are  25  per  cent,  and  of  pumping  systems  75 
per  cent;  the  75  per  cent  of  pumping  systems  is  divided  into 
15  per  cent  which  pump  to  distributing  reservoirs  and  60  per 
cent  which  pump  into  the  pipes  either  with  or  without  tanks 
or  stand-pipes.  It  is  thus  seen  that  the  pumping  systems  are 
about  three  times  as  many  as  the  gravity  systems,  and  that 
the  systems  of  direct  pumping  include  over  one-half  the  total 
number. 

In  the  New  England  states,  and  also  in  the  Pacific  states, 
the  number  of  gravity  systems  is  about  the  same  as  that  of 
the  pumping  systems.  In  the  central  and  northwestern 
states,  however,  the  number  of  pumping  systems  is  twenty 
or  thirty  times  as  great  as  that  of  the  gravity  systems.  In  any 
particular  case  the  local  conditions  determine  the  system  to 
be  used,  that  being  selected  which  gives  the  best  and  purest 


32.  CONSUMPTION   OF  WATER.  89 

supply  at  the  minimum  cost  of  construction  and  operation. 
The  expense  of  construction  is  greatest  for  a  gravity  system, 
and  the  expense  of  operation  is  greatest  for  a  pumping  sys- 
tem. 

32.  CONSUMPTION  OF  WATER. 

The  amount  of  water  used  in  a  town  depends  mainly  upon 
its  population,  but  also  upon  the  habits  and  occupations  of 
the  people.  In  designing  a  water-works  it  is  customary  to 
estimate  the  mean  daily  consumption  per  person  and  then  to 
multiply  this  by  the  present  or  prospective  population  in 
order  to  find  the  probable  mean  amount  that  will  be  required. 
For  this  purpose  the  records  of  towns  of  similar  character 
having  water-works  in  operation  for  several  years  are  to  be 
consulted.  As  a  rough  estimate  for  approximate  computa- 
tions 100  gallons  per  person  per  day  may  be  taken  as  a  mean 
figure.  The  gallon  used  in  this  book  is  the  American  gallon 
of  231  cubic  inches. 

Ancient  Rome  had  a  daily  supply  of  about  50  gallons  per 
person.  Modern  European  cities  rarely  exceed  this  amount. 
London  uses  44  gallons  per  person  per  day,  Paris  36  gallons, 
Berlin  30  gallons,  while  smaller  cities  like  Geneva  and 
Hanover  use  only  about  25  gallons.  Undoubtedly  50  gal- 
lons per  person  is  an  ample  daily  allowance,  and  the  fact  that 
the  consumption  of  American  cities  is  so  much  greater  must 
be  ascribed  to  waste  rather  than  to  reasonable  use. 

The  mean  daily  consumption  per  person  in  Philadelphia 
was  68  gallons  in  1880  and  132  gallons  in  1890;  in  Chicago, 
112  gallons  in  1880  and  127  gallons  in  1890;  in  St.  Louis,  72 
gallons  in  1880  and  78  gallons  in  1890;  in  Detroit,  130  gallons 
in  1880  and  155  gallons  in  1890.  In  general  the  consumption 
of  water  shows  a  gradual  increase  in  all  the  cities  of  the 
United  States,  but  according  to  reliable  estimates  nearly  one- 
half  this  is  waste.  This  is  demonstrated  by  the  use  of  the 


90  WATER-SUPPLY   SYSTEMS.  III. 

meter  plan,  in  which  payment  is  made  only  for  the  actual 
amount  of  water  drawn  from  the  pipes;  thus  meters  placed  in 
a  number  of  first-class  apartment  houses  in  Boston  registered 
about  5  I  gallons  per  person  per  day,  while  those  in  moderate- 
class  apartment  houses  showed  32  gallons,  and  in  the  lowest- 
class  apartment  houses  only  17  gallons. 

A  small  city  generally  uses  less  water  per  person  than  a 
large  one;  but  the  mean  for  American  cities  having  50000 
population  is  over  100  gallons  per  person  per  day.  A  manu- 
facturing town  has  a  high  rate  of  consumption,  and  the  same 
is  true  for  a  city  with  asphalt  streets,  since  much  water  is  used 
in  washing  them.  In  towns  without  factories  and  having  a 
population  of  less  than  10000  the  mean  daily  consumption 
will  generally  be  between  60  and  100  gallons  per  person  per 
day. 

The  daily  consumption  during  July  and  August  is  from  15 
to  20  per  cent  greater  than  the  mean  for  the  year,  as  in  these 
months  much  water  is  used  for  sprinkling  streets  and  lawns. 
In  the  northern  part  of  the  United  States  the  daily  consump- 
tion during  January  and  February  may  be  also  15  or  20  per 
cent  higher  than  the  mean,  owing  to  the  large  amount  that 
is  wasted  in  order  to  prevent  freezing  of  the  pipes.  If  100 
gallons  per  person  is  the  daily  mean  for  the  year  the  daily 
mean  during  these  four  months  may  be  as  high  as  120  gallons 
per  person. 

On  Mondays,  when  every  household  is  at  work  on  the 
weekly  washing,  the  consumption  may  be  put  at  from  20  to 
40  per  cent  higher  than  the  mean  for  the  week.  Accordingly, 
on  the  basis  of  100  gallons  per  person  as  the  daily  mean  for 
the  year,  the  Monday  consumption  during  very  cold  or  very 
hot  weather  may  be  taken  as  from  140  to  170  gallons  per 
person  per  day. 

The  amount  required  to  extinguish  fires  is  small  when 
expressed  as  a  daily  mean,  but  an  average  fire  requires  about 


33.         CAPACITY  OF  STORAGE  RESERVOIRS.          91 

three  hydrant  streams,  each  delivering  200  gallons  per  minute. 
If  two  fires  occur  simultaneously  in  a  town  or  fire  district  of 
10  ooo  people  the  hourly  consumption  for  fire  purposes  alone 
will  be  at  the  rate  of  173  gallons  per  person  per  day.  In 
general  for  each  fire  district  the  maximum  available  hourly 
supply  for  both  fire  purposes  and  domestic  use  should  be  at  a 
rate  from  three  to  four  times  as  great  as  that  of  the  mean 
daily  consumption. 

The  pressure  under  which  the  water  is  delivered  in  the 
streets  is  an  important  factor  in  all  questions  relating  to  fires. 
If  the  pressure  be  very  high  fire  engines  may  not  be  needed, 
as  the  hose  may  be  attached  directly  to  the  hydrants.  If  the 
pressure  be  very  low  it  may  not  be  possible  to  secure  an 
effective  fire  service  even  with  the  use  of  engines,  since  a  low 
pressure  is  always  accompanied  by  a  small  discharge.  In  the 
houses  a  very  high  pressure  greatly  increases  the  waste  of 
water,  while  of  course  a  very  low  pressure  furnishes  an  insuffi- 
cient supply.  Pressures  over  100  pounds  per  square  inch  are 
high,  and  pressures  less  than  30  pounds  per  square  inch  are 
low. 

33.  CAPACITY  OF  STORAGE  RESERVOIRS. 

When  plans  are  to  be  made  for  a  gravity  supply  there  are 
two  important  preliminary  questions  to  be  discussed:  first, 
what  amount  of  water  can  be  obtained;  second,  what  storage 
capacity  is  needed  for  the  supply  of  the  town.  The  first 
question  involves  the  preparation  of  maps  of  the  neighboring 
watersheds,  the  collection  of  rainfall  and  run-off  data,  and 
certain  reservoir  estimates.  The  second  question  involves  the 
considerations  of  consumption  and  pressure  presented  in  the 
last  article  and  more  detailed  estimates  of  storage  capacity. 
The  combination  of  the  results  of  these  two  inquiries  enables 
a  decision  to  be  made  as  to  whether  or  not  a  given  watershed 
will  furnish  a  sufficient  supply  for  the  town.  All  the  discus- 


WATER-SUPPLY   SYSTEMS. 


III. 


sions  of  the  last  chapter  regarding  purity  of  the  water  should 
also  receive  careful  attention  during  the  progress  of  the 
inquiry. 

As  an  example,  suppose  that  a  town  of  6000  people,  situated 
at  A,  on  a  stream  too  impure  for  domestic  purposes,  requires 
estimates  to  be  made  for  obtaining  a  gravity  supply  by  build- 


WATERSHED. 

ing  a  reservoir  at  B  to  impound  the  run-off  of  a  brook.  From 
surveys  and  maps  the  area  of  the  watershed  above  B  is  found 
to  be  1390  acres.  The  mean  annual  rainfall  is  known  to  be 
38  inches,  of  which  about  45  per  cent  is  run-off,  the  remainder 
going  into  evaporation  and  percolation,  and  hence  the  mean 
annual  available  storage  is  647  ooo  ooo  gallons.  The  mini- 
mum annual  rainfall,  however,  is  31  inches,  and  in  such  a 
year  the  available  storage  will  be  528  ooo  ooo  gallons,  or  say 
a  mean  daily  supply  of  about  I  400  ooo  gallons,  which  is  more 
than  200  gallons  per  person.  The  flow  of  the  brook  at  the 
driest  season  is  found  by  measurement  or  estimation  to  be 
150000  gallons  per  day,  or  25  gallons  per  person.  It  is 
accordingly  clear  that  enough  water  can  be  obtained  for  the 
supply  of  the  town  if  sufficient  reservoir  capacity  be  pro- 
vided. 

To  estimate  the  capacity  required,  suppose  that  July  is  a 
wet  month,  August  a  dry  month,  and  September  a  very  dry 


33-  CAPACITY   OF   STORAGE   RESERVOIRS.  93 

month.  Then  during  July  the  reservoir  must  store  a  quantity 
ample  to  supply  the  September  demand.  Let  the  mean  daily 
consumption  during  August  and  September  be  100  gallons 
per  person,  or  a  total  of  600  ooo  gallons,  and  let  the  average 
daily  run-off  be  400000  gallons  in  August  and  150000  in 
September.  If  the  reservoir  is  full  at  the  end  of  July  it  will 
not  be  full  at  the  end  of  August,  as  the  supply  is  200  ooo  gal- 
lons less  than  the  consumption;  in  September,  moreover,  the 
daily  run-off  received  is  450  ooo  gallons  less  than  the  con- 
sumption. Accordingly,  if  the  reservoir  is  to  be  half-full  at 
the  end  of  September  it  must  have  a  capacity  of  39  400  ooo 
gallons. 

The  result  of  the  preliminary  inquiry  in  this  case  is  that  a 
sufficient  supply  for  the  driest  season  will  be  furnished  by  the 
watershed  above  B,  provided  that  a  reservoir  holding  about 
40  ooo  ooo  gallons  be  constructed.  To  ascertain  if  such  a 
reservoir  is  feasible  a  detailed  survey  of  the  site  must  be  made 
and  a  map  be  drawn  showing  contours  for  every  foot  of  ver- 
tical height.  From  this  map  the  height  and  size  of  the 
necessary  dams  are  determined,  and  then  borings  are  made  to 
ascertain  the  character  of  the  foundations  which  these  con- 
structions require.  Plans  for  the  dam  and  its  waste-weir,  the 
pipe  lines,  distributing  reservoirs,  and  street  mains  are  also 
prepared,  and  finally  an  estimate  of  cost  of  the  proposed 
gravity  system  is  made.  After  the  engineer  has  finished  this 
work  and  made  his  report  it  remains  for  the  town  authorities 
to  decide  whether  the  money  can  be  raised  to  carry  out  the 
execution  of  the  project. 

In  this  illustrative  case  the  reservoir  capacity  required  is 
about  80  times  the  mean  daily  consumption.  This  ratio  is 
generally  exceeded  in  the  gravity  systems  of  cities;  thus  in 
1897  New  York  had  a  storage  capacity  of  38  ooo  ooo  ooo  gal- 
lons and  a  mean  daily  consumption  of  230000000  gallons, 
giving  a  ratio  of  about  165  ;  some  other  cities  have  a  ratio 


94  WATER-SUPPLY   SYSTEMS.  III. 

higher  than  200,  while  some  small  cities  and  towns  run  below 
100  and  occasionally  below  50. 

It  is  not  easy  to  collect  the  data  for  an  estimate  of  reser- 
voir capacity,  properly  coordinate  them,  and  draw  correct 
conclusions;  in  fact  it  requires  the  training  and  good  judg- 
ment of  an  experienced  engineer  to  arrive  at  a  sure  decision. 
Other  elements  than  those  above  outlined  are  also  to  receive 
attention,  such  as  evaporation  from  the  surface  of  the  reser- 
voir and  the  increase  of  supply  due  to  the  growth  of  the 
town.  Estimates  for  several  watersheds  may  have  to  be 
made  and  compared,  and  perhaps  in  the  above  case  it  might 
be  cheaper  to  construct  filter  galleries  or  filter  beds  to  purify 
the  river  water  arid  distribute  it  by  a  pumping  system  than  to 
carry  out  the  proposed  gravity  supply.  Anyone  may  make 
rough  comparisons,  but  only  the  engineer  can  prepare  such 
plans  and  estimates  that  a  sure  determination  can  be  formed 
regarding  the  system  which  will  furnish  a  pure  and  abundant 
supply  and  yet  be  the  most  economical  in  construction  and 
maintenance. 

34.  RESERVOIR  DAMS  OF  EARTH. 

Earthen  reservoir  dams  have  been  built  since  the  most 
ancient  times  and  are  still  extensively  used.  When  rock 
foundation  is  not  at  hand  a  masonry  structure  is  impracticable, 
and  an  earthen  embankment  must  necessarily  be  built.  The 
figure  shows  a  cross-section  illustrating  one  of  the  best  forms 
of  construction.  AB  is  the  natural  surface  of  the  ground, 
and  the  trench  CD  is  carried  down  several  feet  lower  than  this 
surface  and  filled  with  concrete  or  puddled  clay,  in  order  to 
prevent  water  from  percolating  under  the  dam.  Above  this 
trench  the  core  is  built  of  carefully  selected  material,  rolled  in 
layers  concave  upward,  and  on  each  side  of  this  core  common 
earth,  usually  called  the  frost  covering,  is  placed.  The  width 
of  the  dam  at  the  top  is  at  least  15  feet,  and  the  width  at  the 


34.  RESERVOIR   DAMS   OF   EARTH.  95 

bottom  depends  upon  the  height;  if  the  height  be   1 8  feet 
the  bottom  width  should  be  75  feet  or  more. 

The  core  is  the  effective  part  of  an  earthen  dam,  and  the 
material  composing  it  should  be  such  as  to  prevent  the  water 
from  passing  through  it.  For  this  purpose  about  5  cart 

E         F 
j* 

Water 


SECTION  OF  AN  EARTHEN  DAM. 

loads  of  gravel  are  mixed  with  2  loads  of  sand  and  I  load  of 
clay.  The  sand  to  a  certain  extent  fills  the  spaces  between 
the  grains  of  gravel,  while  the  smaller  interstices  are  filled 
by  the  clay;  thus  when  mixed  and  thoroughly  rolled  the  8 
loads  occupy  a  volume  equal  to  about  6  original  loads.  The 
material  must  be  kept  well  sprinkled  during  the  rolling  and 
the  middle  of  each  layer  be  kept  somewhat  lower  than  the 
sides.  Instead  of  a  core  a  thick  wall  of  puddled  clay  is  fre- 
quently used  to  prevent  percolation. 

The  frost  covering  of  earth  is  applied  simultaneously  with 
the  construction  of  the  core.  This  earth  is  any  kind  that 
may  be  at  hand,  as  its  office  is  not  to  prevent  percolation  of 
water,  but  merely  to  protect  the  core.  The  front  slope  BF 
is  about  2  to  I,  that  is,  2  feet  of  horizontal  projection  to 
I  foot  of  vertical  projection,  and  it  should  be  covered  with 
grass.  The  back  slope  has  a  berm  G  just  above  low  water, 
and  this  is  wide  enough  so  Jthat  a  cart  may  run  along  it  to 
make  repairs.  The  slope  AG  is  2  to  I  or  3  to  I,  and  it  is 
covered  with  riprap;  the  slope  GE  is  about  2\  to  I,  and  this 
is  paved  with  thick  stones,  in  order  to  prevent  injury  from 
the  action  of  waves  and  ice. 


96  WATER-SUPPLY   SYSTEMS.  III. 

If  water  runs  over  the  top  of  an  earthen  dam  its  destruc- 
tion surely  follows,  and  hence  a  waste-weir  or  wasteway 
should  be  provided  to  carry  off  the  excess  of  water;  these 
will  be  discussed  in  Art.  36.  Failures  have  also  occurred  by 
the  percolation  of  water  along  the  pipes  which  pass  through 
the  dams;  to  prevent  this  a  good  plan  is  to  build  a  masonry 
culvert  for  carrying  the  pipes,  the  exterior  surface  of  the 
culvert  being  rough  and  earth  being  puddled  around  it. 

In  1874  occurred  the  failure  of  an  earthen  reservoir  dam 
at  Williamsburg,  Mass.,  causing  great  damage  to  property 
in  the  valley  below  and  the  loss  of  143  lives.  The  dam  was 
about  550  feet  long,  43  feet  high  at  the  middle,  16  feet  wide 
at  the  top,  and  with  side  slopes  of  ij  to  I.  There  was  no 
core  such  as  described  above,  but  instead  a  rubble  wall  2  feet 
thick  at  the  top  and  6  feet  thick  at  the  base  was  built 
through  the  middle.  It  was  shown  that  this  wall  was  of  a 
rude  character  and  imperfectly  filled  with  mortar  of  a  poor 
quality,  and  that  its  foundation  was  particularly  defective, 
so  that  the  percolation  of  water  through  and  under  it  was 
the  cause  of  the  failure. 

In  1889  one  of  the  greatest  disasters  on  record  occurred 
by  the  failure  of  an  earthen  dam  at  the  South  Fork  reser- 
voir near  Johnstown,  Pa.,  2142  lives  being  lost  and  property 
destroyed  whose  value  was  3  500  ooo  dollars.  The  reservoir 
covered  407  acres  and  the  watershed  area  was  48.6  square 
miles.  The  dam  was  about  18  feet  wide  at  the  top,  with  a 
slope  of  i £  to  i  on  the  lower  side  and  2  to  I  on  the  upper  side; 
the  height  was  about  70  feet  and  the  width  at  the  base  about 
265  feet.  It  was  shown  that  failure  occurred  not  through 
any  fault  of  construction  of  the  main  body  of  the  dam,  but 
entirely  by  reason  of  the  insufficient  size  of  the  wasteway. 
This  had  been  planned  to  be  150  feet  in  width  and  10  feet 
in  depth  below  the  top  of  the  dam,  but  as  constructed  its 
effective  width  was  only  70  feet  and,  owing  to  the  top  of  the 
dam  having  been  subsequently  lowered  in  height,  its  depth 


35.  RESERVOIR  DAMS  OF  MASONRY.  c# 

only  8  feet.  During  May  30  and  31  the  rainfall  on  the 
watershed  was  between  6  and  8  inches,  and  for  several  hours 
the  rate  was  greater  than  f  inches  per  hour.  The  insufficient 
size  of  the  waste-weir  caused  the  water  level  in  the  reservoir 
to  gradually  rise  until  at  11:30  A.M.  on  May  31  it  began  to 
run  over  the  top  of  the  earthen  dam.  At  2  155  P.M.  a  portion 
of  the  dam,  400  feet  wide  at  the  top  and  40  feet  deep,  broke 
away  and  a  Vertical  wall  of  water  30  feet  high  swept  down 
the  narrow  valley,  destroying  entire  villages  in  its  course.  At 
3:12  P.M.  this  flood  of  water  reached  the  city  of  Johnstown, 
12  miles  down  the  stream  and  250  feet  lower  than  the  reser- 
voir, and  there  in  a  few  minutes  direful  death  and  destruction 
were  wrought. 

It  is  an  old  saying  that  one  failure  teaches  more  than  many 
successes.  Certainly  these  two  failures  of  earthen  dams 
teach  most  emphatically  two  important  lessons:  first,  that  the 
construction  of  the  dam  and  its  foundations  must  be  such  as 
to  prevent  the  percolation  of  water  through  or  under  it; 
second,  that  the  width  and  depth  of  the  waste-weir,  or  spill- 
way, must  be  sufficient  to  discharge  the  accumulations  of  a 
very  heavy  rainfall.  To  secure  these  results  plans  alone  are 
not  enough,  but  constant  and  vigilant  inspection  of  every 
phase  of  the  work  is  required.  As  a  consequence  of  these 
disasters  boards  of  engineers  have  been  instituted  in  some 
states  to  make  annual  examinations  of  reservoirs  and  recom- 
mend such  improvements  as  they  judge  necessary  for  the 
public  safety. 

35.  RESERVOIR  DAMS  OF  MASONRY. 

Earthen  dams  far  outnumber  those  of  masonry,  since  the 
latter  can  only  be  constructed  when  a  rock  foundation  is  at 
hand.  The  rock  must  be  entirely  exposed,  and  be  cut  into 
trenches  and  steps,  so  that  the  dam  may  be  thoroughly  bonded 
with  the  rock,  and  thus  all  percolation  of  water  be  prevented. 


98  WATER-SUPPLY    SYSTEMS.  III. 

The  beds  and  joints  of  all  the  stones  are  to  be  entirely  filled 
with  hydraulic  cement,  and  the  bonding  is  to  be  such  that  no 
contiguous  horizontal  joints  are  formed,  in  order  that  there 
may  be  no  liability  to  sliding  under  the  water  pressure. 

The  shape  of  the  cross-section  of  the  dam  will  depend  upon 
its  height;  when  the  height  is  less  than  60  feet  the  trapezoidal 

form  is  commonly  used.  The  back 
of  the  dam  where  the  water  pressure 
is  applied  may  be  vertical  or  have  a 
slight  batter,  but  the  front  has 
always  a  considerable  batter.  The 
thickness  of  the  top  of  the  dam 
ranges  from  4  feet  for  low  heights 
up  to  15  feet  or  more  for  heights  of 
100  feet.  The  batter  of  the  back 
and  the  thickness  of  the  top  being 

assumed,  the  thickness  of  the  base 
SECTION  OF  MASONRY  DAM. 

is  to  be  computed  so  that  there  may 
be  ample  security  to  resist  the  overturning  action  of  the  water. 

The  figure  shows  the  forces  acting  on  a  dam.  The  horizon- 
tal water  pressure  P  is  balanced  by  an  equal  resisting  force 
P  acting  along  the  base  AB.  The  weight  of  the  dam,  consist- 
ing of  the  weights  of  the  parallelogram  and  two  triangles,  is 
^i  +  V\  +  ^i»  and  this  is  balanced  by  an  equal  upward  resist- 
ance V.  It  is  shown  in  treatises  on  construction  that  ample 
security  will  obtain  when  the  thickness  of  the  base  is  such 
that  the  distance  from  V  to  the  toe  B  is  one-third  of  the  total 
thickness.  Then,  from  the  principle  of  mechanics  that  the 
sum  of  the  moments  of  all  the  forces  causing  right-handed 
rotation  around  B  must  equal  the  sum  of  the  moments  of 
those  causing  left-handed  rotation,  this  thickness  b  is  com- 
puted. 

The  horizontal  water  pressure  Ptor  a  dam  one  foot  in  length 
is  shown  by  hydrostatics  to  be  3i.25//a  pounds  if  the  dam  be 
h  feet  in  height.  The  point  of  application  of  this  pressure  is 


35-  RESERVOIR   DAMS   OF   MASONRY.  99 

\h  above  the  base  of  the  dam.  For  example,  let  a  dam  be 
48  feet  high,  then  the  horizontal  pressure  against  one  foot  of 
its  length  is  72  ooo  pounds  and  the  height  of  its  point  of 
application  above  the  base  is  16  feet. 

Let  a  masonry  dam  48  feet  high  and  I  foot  long  weigh 
150  pounds  per  cubic  foot  and  have  a  top  thickness  of  8  feet 
and  a  back  batter  of  I  inch  to  I  foot.  Then  the  base  of  the 
first  triangle  is  4  feet,  its  area  96  square  feet,  and  the  weight 
Vl  is  14  400  pounds.  The  area  of  the  parallelogram  is  384 
square  feet  and  the  weight  F,  is  57  600  pounds.  The  base  of 
the  front  triangle  is  (b  —  8  —  4)  feet,  its  area  is  2^(b  —  12) 
pounds,  and  the  weight  F3  is  $6oo(b  —  12)  pounds.  The 
total  weight,  which  is  equal  to  the  upward  reaction  F,  is 
hemce  72  ooo  +  $6oo(b  —  12)  pounds. 

Taking  B  as  a  center  of  moments,  the  lever  arm  of  P  is  16, 
that  of  F,  is  b  —  2|,  that  of  F3  is  b  —  8,  that  of  V,  is 
%(b  —  12),  and  that  of  V  is  \b.  The  forces  P  and  V  cause 
right-handed  rotation  around  B,  and  the  sum  of  their 
moments  is 

72  ooo  X  1 6  +  [72  ooo  +  36oo(£  —  12)]  x  \b ; 

the  forces  F,,  Fa,  and  F,  cause  left-handed  rotation  around  B, 
and  the  sum  of  their  moments  is 

14400  X  (b— 2|)+  57  600  X  (b—  8)  +  36oo(£-  i2)xf(£—  12). 
Equating  these  two  expressions  and  solving  for  b  there  is 
found  31  feet  as  the  required  thickness  of  the  base.  The 
batter  of  the  front  slope  will  therefore  be  4!  inches  to  each 
vertical  foot. 

The  front  of  a  masonry  dam  is  frequently  built  with  a  less 
batter  at  the  top  than  at  the  bottom,  thus  forming  a  broken 
or  curved  profile.  For  dams  greater  than  100  feet  in  height 
this  is  the  general  practice,  as  it  is  necessary  in  order  that  the 
stress  on  the  stone  near  the  toe  B  may  not  be  too  great.  For 
very  high  dams  the  back  is  also  curved  in  its  lower  portion. 
The  design  of  these  structures  requires  very  elaborate  com- 


100  WATER-SUPPLY  SYSTEMS.  III. 

putations,  and  these  will  be  found  explained  in  special  treatises 
on  engineering  construction. 

The  principles  governing  concrete  dams  are  the  same  as 
those  for  stone  dams.  Among  the  high  dams  is  the 
concrete  structure  at  San  Mateo,  Cal.,  which  impounds 


SAN  MATEO  CONCRETE  DAM. 

the  reservoir  for  the  water  supply  of  San  Francisco.  Its 
height  when  completed  is  to  be  170  feet  and  the  top  thickness 
25  feet;  the  base  thickness  is  176  feet.  The  batter  of  the 
back  is  3  inches  to  I  foot,  that  of  the  front  is  about  5  inches 
per  foot  for  a  depth  of  70  feet  from  the  top,  and  then  follows 
a  curve  of  258  feet  radius,  as  shown  in  the  figure.  The  length 
of  the  dam  is  680  feet  on  top,  and  it  is  curved  in  plan  so  as 
to  give  an  apparent  increase  in  stability  by  virtue  of  the  arch 
action.  The  concrete  blocks  near  the  base  are  very  large,  and 
they  are  made  of  a  ^f  shape,  so  as  to  thoroughly  interlock. 

Among  the  largest  stone  dams  in  the  United  States  are  the 
Cheesman  dam  in  Colorado,  completed  in  1904,  which  has  a 
maximum  height  of  230  feet,  and  the  Wachusett  dam  in  Mas- 
sachusetts, completed  in  1905,  which  has  a  maximum  height  of 
228  feet.  One  of  the  highest  dams  in  the  world  is  the  new 


36. 


WASTE-WEIRS   AND1 


IOI 


Croton  dam,  completed  in  1906,  on  the  water  supply  for 
New  York  city,  its  greatest  height  above  the  foundation  being 
297  feet.  The  Kensico  dam,  built  1915,  contains  more  masonry 
than  any  structure  in  the  world  except  the  great  pyramid. 


36.  WASTE-WEIRS  AND  PIPE  CONNECTIONS. 

A  waste-weir  is  an  opening  in  the  top  of  a  dam  to  prevent 
the  water  from  rising  as  high  as  the  top.  A  masonry  dam  is 
often  built  without  a  waste-weir,  for  no  damage  is  done  by 
allowing  the  water  to  flow  over  the  top  if  the  bed  of  the  valley 
for  some  distance  below  it  be  of  rock,  so  that  undermining  of 
foundations  cannot  occur.  For  all  earthen  dams  of  storage 
reservoirs,  however,  a  waste-weir,  or  wasteway,  is  absolutely 
necessary. 

A  waste-weir  notch  is  in  the  top  of  a  masonry  construction 
built  at  one  end  of  the  dam.  This  masonry  construction  is 
in  fact  a  masonry  dam,  usually  of  low  height,  the  top  being 
on  the  same  level  as  the  dam.  Thus,  in  the  figure,  DD  repre- 


SECTIONS  OF  A  MASONRY  WASTE-WEIR. 

sents  the  top,  A  A  the  sill  of  the  waste-weir,  and  AC  the 
depth  of  water  flowing  over  the  weir.  The  width  of  the  dam 
on  the  sill  is  A3  in  the  sectional  view,  where  A C  also  shows 
the  depth  of  the  overflow.  Let  b  be  the  width  AA  and  H 
the  depth  AC\  then,  if  b  and  H  be  in  feet  it  is  shown  in 
hydraulic  literature  that  the  discharge  in  cubic  feet  per  second 
is  given  by  q  =  3.06^/7*.  From  this  formula  the  proper  size 
of  a  waste-weir  notch  can  be  determined  when  the  discharge 
q  is  known. 


>»••'•  1  -•>  ^  v»i  *•%'%' 

['  "'WATE.PnSt 


102  '  "'WATE.PnStPLY   SYSTEMS.  III. 

When  a  heavy  rainfall  occurs  over  the  watershed  the  waste- 
weir  should  be  able  to  discharge  in  one  hour  whatever  part 
may  reach  the  reservoir  in  that  time.  The  longer  such  a 
rainfall  continues  the  nearer  should  the  discharging  capacity 
of  the  waste-weir  approach  to  the  amount  of  rainfall  on  the 
watershed.  For  a  large  watershed  a  waste-weir  designed  to 
discharge  one-third  of  an  inch  per  hour  on  that  watershed  will 
generally  give  ample  security,  but  for  a  small  one,  where  the 
flood  run-off  occurs  quickly,  a  somewhat  higher  figure  should 
be  taken. 

As  an  example,  the  data  of  the  watershed  shown  in  the 
figure  of  Art.  34  may  be  used.  The  watershed  area  is  1390 
acres,  and  supposing  a  rainfall  of  one  inch  per  hour  to 
occur  and  that  six-tenths  of  this  reaches  the  reservoir  in  one 
hour,  the  waste-weir  must  be  sufficiently  large  to  allow  840 
cubic  feet  per  second  to  pass  over  it.  If  the  sill  of  the  weir 
be  4  feet  below  the  top  of  the  dam,  then  H  =  4  feet;  and 
taking  q  =  840,  the  formula  gives  b  =  34.3  feet  as  the  width 
AA  required.  If  //"is  to  be  5  feet,  however,  then  the  width 
b  is  24.8  feet.  It  is  here  seen  that  the  determination  of  the 
data  is  the  hardest  part  of  the  problem  of  designing  the  size 
of  a  waste-  weir. 

When  rock  is  found  at  one  end  of  the  dam  a  canal  may  be 
cut  through  it,  and  this  arrangement  is  called  a  wasteway. 
At  the  South  Fork  dam,  whose  failure  was  described  in  Art. 
34,  the  wasteway  was  176  feet  long,  the  width  at  entrance  120 
feet  and  at  outfall  69  feet,  while  the  horizontal  bed  was  8  feet 
below  the  top  of  the  dam.  The  above  formula  may  also  be 
applied  to  this  case,  taking  H  =  8  feet  and  b  =  69  feet,  from 
which  it  is  found  that  when  the  water  was  at  the  level  of  the 
top  of  the  dam  the  discharge  q  was  about  4780  cubic  feet  per 
second.  The  wasteway*  was,  however,  obstructed  by  fish 
screens,  so  that  probably  the  actual  discharge  was  only  about 
4000  cubic  feet  per  second,  while  the  amount  entering  the 
reservoir  was  about  8000  cubic  feet  per  second. 


37.  AQUEDUCTS.  103 

The  water  pipes  that  run  into  a  reservoir  through  an 
earthen  dam  should  terminate  in  a  gate  chamber  which  is 
provided  with  valves  for  admitting  and  shutting  off  the  flow. 
This  gate  chamber  may  be  arranged  so  as  to  admit  the  water 
to  it  at  different  levels,  for  at  certain  seasons  the  water  may 
be  purer  at  one  depth  than  at  another.  These  openings  are 
provided  with  screens  to  keep  out  fish.  The  gate  chamber  is 
necessarily  of  masonry,  and  it  is  hence  generally  built  near 
one  end  of  the  dam  where  a  good  foundation  may  be  obtained, 
and  it  often  forms  a  part  of  the  waste-weir  structure. 

An  arched  culvert  extended  through  the  embankment  is 
one  of  the  best  ways  for  bringing  the  pipes  to  the  gate  cham- 
ber, a  thick  stop  wall  being  built  at  the  upper  end  to  keep 
the  water  out  of  it.  The  exterior  of  the  arch  stones  should 
be  left  rough  and  puddled  clay  be  rammed  around  them,  so 
as  to  prevent  all  percolation  of  water.  This  culvert  carries 
not  only  the  water  main,  but  also  a  smaller  pipe  which  may  be 
used  to  draw  off  the  reservoir  when  repairing  or  cleaning  is  to 
be  done. 

In  all  the  masonry  work  of  waste-weirs,  gate  chambers,  and 
culverts  hydraulic  mortar  of  the  best  quality  must  be  used 
and  an  efficient  inspection  be  maintained  to  secure  good 
material  and  workmanship.  The  strength  of  a  structure  is 
the  strength  of  it  weakest  part,  and  hence  if  one  part  be 
defective  through  lack  of  proper  inspection  the  security  of  the 
entire  structure  is  correspondingly  lowered. 

37.  AQUEDUCTS. 

The  water  of  a  storage  reservoir  is  carried  to  the  distribut- 
ing reservoirs  by  canals,  aqueducts,  or  pipe  lines.  A  canal  is 
advantageous  because  it  gives  opportunity  for  the  aeration  of 
the  water,  but  disadvantageous  on  account  of  the  losses  due 
to  evaporation  and  percolation,  as  also  on  account  of  the 
liability  to  pollution;  hence  canals  are  rarely  used.  An 


IO4 


WATER-SUPPLY   SYSTEMS. 


III. 


aqueduct  is  an  artificial  channel  constructed  in  masonry,  but 
its  top  is  covered;  like -a  canal,  it  is  laid  out  on  a  uniform 
slope,  and  unlike  a  pipe,  it  is  never  completely  filled  by  the 
flowing  water.  The  famous  Roman  aqueducts  were  carried 
across  valleys  on  masonry  arches  in  order  to  preserve  a  uniform 
slope;  they  were  of  rectangular  cross-section,  lined  with  con- 
crete, and  covered  with  either  stone  slabs  or  arched  roofs. 
Aqueducts  are  now  built  only  for  the  supply  of  large  cities,  a 
pipe  line  being  sufficient  to  carry  it  in  ordinary  cases;  they 
are  built  below  the  surface  of  the  ground  and  are  carried 
through  rock  in  tunnels.  The  word  conduit  is  often  used  as 
synonymous  with  aqueduct,  but  it  also  applies  to  any  large 
covered  channel  for  carrying  water. 

The  cross-sections  used  for  modern  aqueducts  are  generally 
of  the  circular  and  the  basket-handle  form.  The  circular  sec- 
tion is  used  for  small  aqueducts  less  than  about  six  feet  in 
diameter.  For  larger  diameters  a  basket-handle  section  with 


CROSS-SECTIONS  OF  AQUEDUCTS. 

vertical  sides  is  used  in  rock  or  in  soil  so  stiff  as  to  exert  little 
lateral  pressure,  while  the  sides  are  inclined  inward-in  common 
earth;  both  of  these  have  the  bottoms  formed  of  circular 
inverts  of  large  radius. 

Brick  or  stone  was  formerly  the  material  generally  used  in 
aqueduct  construction,  but  now  concrete  is  more  usually  em- 
ployed. In  all  yielding  soil  there  must  be  provided  foundations 
of  piles  or  concrete, in  order  to  prevent  settling.  For  the  smaller 
circular  sections  cast  iron  or  steel  is  used  instead  of  masonry. 

A  masonry  aqueduct  is  rarely  filled  with  water  up  to  the 
top,  because  it  is  not  adapted  to  withstand  a  high  outward 


37- 


AQUEDUCTS. 


105 


water  pressure,  but  an  iron  or  steel  one  may  be  entirely  filled 
if  desired.  In  general,  however,  the  word  aqueduct  implies 
that  the  water  has  a  free  surface. 

The  quantity  of  water  that  an  aqueduct  will  deliver  depends 
upon  the  area  of  its  cross-section,  upon  the  surface  in  contact 
with  water,  and  upon  the  longitudinal  slope.  Let  a  be  the 
area  of  the  cross-section,  v  the  mean  velocity  of  flow  per 
second,  and  q  the  discharge  per  second;  then  q  =  av.  Now 
let/  be  the  length  of  the  wetted  perimeter,  that  is,  the  length 
of  the  inner  part  of  the  cross-section  which  is  in  contact  with 
the  water;  then  a  -±- p  is  called  the  hydraulic  radius  of  the 
cross-section  and  is  designated  by  r.  Let  /  be  any  length  of 
the  aqueduct  in  which  the  vertical  fall  is  h\  then  h  -r-  /  is 
called  the  slope  and  is  designated  by  s.  The  formula  for  the 
velocity  v  may  now  be  stated  as  v  =  c  Vrs,  in  which  c  is  a 
number  which  depends  upon  the  roughness  of  the  surface  and 
other  circumstances.  If  the  surface  were  perfectly  smooth 
the  mean  velocity  v  would  continually  increase,  but  owing  to 
the  friction  caused  by  the  roughness  it  remains  constant 
unless  r  and  s  change  in  value. 

The  value  of  the  coefficient  c  is  to  be  found  by  consulting 

the    discussions   of    recorded   gagings    given   in    treatises    on 

hydraulics.      If  the  aqueduct  has  a  cement  lining,  and  r  be 

taken  in  feet  and  v  in  feet  per  second,  the  following  values  of 

COEFFICIENTS  FOR  AQUEDUCTS. 


Hydraulic 

Radius 

s  =  0.00005 

J  =  0.0001 

S  =  0.0002 

s  =  0.0004 

S  =  O.OOI 

in  Feet. 

r  —  I 

114 

120 

123 

125 

127 

r=  1.5 

126 

130 

133 

135 

136 

r  =  2 

135 

138 

140 

141 

142 

r  =  3 

147 

148 

149 

149 

150 

c  may  be  employed.      For  example,  if  an  aqueduct  be  laid  on 
a  slope  of  one  foot  per  mile  the  value  of  s  is  1/5280  = 


IO6  WATER-SUPPLY   SYSTEMS.  III. 

0.0001894;  if  its  cross-section  be  48  square  feet  and  its  inner 
perimeter  25  feet  the  value  of  r  when  running  full  is  1.92 
feet;  then  from  the  table  the  coefficient  c  has  the  value  139. 

The  capacity  of  an  aqueduct  is  its  maximum  discharge,  and 
this  occurs  when  it  is  nearly  but  not  quite  full.  For  the  case 
where  the  slope  s  is  0.0001894,  the  hydraulic  radius  r  =  1.92 
feet,  and  c  =  139  the  mean  velocity  v  is  found  by  computa- 
tion to  be  2.65  feet  per  second.  Then  the  discharge  q  is 
127.2  cubic  feet  per  second,  or  82  200000  gallons  per  day; 
this  capacity  is  sufficient  for  the  supply  of  a  city  of  500  ooo 
people.  If  the  slope  of  this  aqueduct  be  4  feet  per  mile  its 
mean  velocity  and  discharge  will  be  double  the  above 
figures;  a  slope  as  great  as  this  is,  however,  very  uncommon, 
although  greater  slopes  are  said  to  have  been  used  in  the  old 
Roman  aqueducts. 

The  old  Croton  aqueduct  for  the  supply  of  New  York,  built 
in  1842,  has  a  cross-section  of  53.3  square  feet,  a  length  of 
38.1  miles,  an  ordinary  slope  of  i.n  feet  per  mile,  and  a 
capacity  of  80  ooo  ooo  gallons  per  day.  The  new  Croton 
aqueduct,  completed  in  1890,  has  a  cross-section  of  about 
160  square  feet  and  a  capacity  of  295000000  gallons  per 
day.  The  aqueduct  for  bringing  the  water  of  the  Catskill 
region  to  New  York  city,  completed  in  1916,  is  the  largest  in 
the  world,  its  cross-section  being  about  240  square  feet,  its 
capacity  about  600  ooo  ooo  gallons  per  day,  and  its  length 
about  92  miles. 

It  is  much  cheaper  to  build  an  aqueduct  than  several  pipe 
lines  of  the  same  capacity;'  for  example,  it  requires  five  or  six 
pipes  of  4  feet  diameter  to  carry  the  same  amount  of  water  as 
one  aqueduct  8  feet  in  diameter,  and  the  cost  of  five  pipe 
lines  would  far  exceed  that  of  the  aqueduct.  The  general 
rule  for  circular  cross-sections  of  the  same  degree  of  smooth- 
ness is  that  the  capacity  varies  as  the  square  root  of  the  fifth 
power  of  the  diameter;  thus,  if  there  be  two  sections  of  2  feet 


38.  PIPE  LINES.  107 

and  8  feet  diameter  the  larger  one  carries  32  times  as  much 
water  as  the  smaller  one. 


38.  PIPE  LINES. 

An  iron  or  steel  pipe  is  adapted  to  stand  the  outward 
pressure  of  water,  and  hence  may  be  carried  down  and  across 
a  valley,  following  the  undulations  of  the  surface,  whereas  an 
aqueduct  must  wind  around  so  as  to  keep  the  slope  nearly 


PIPE  LINE  FROM  STORAGE  TO  DISTRIBUTING  RESERVOIR. 

uniform.  Thus,  if  A  be  a  storage  and  B  a  distributing  reser- 
voir the  pipe  line  ACDCB  is  laid  on  the  shortest  practicable 
route.  The  ancient  Romans  were  not  ignorant  of  the  fact 
that  this  could  be  done,  as  some  suppose,  but  they  had  no 
iron  or  steel  pipes,  and  hence  were  compelled  to  use  the 
aqueduct  method. 

Cast  iron  pipes  are  the  most  common  and  may  be  obtained 
of  any  diameter  up  to  5  feet;  each  pipe  is  12  feet  long,  one 
end  having  a  bell-like  flange  into  which  the  end  of  the  next 
pipe  is  placed  and  rendered  water-tight  by  a  lead  joint. 
Steel  pipes  are  made  in  sections,  each  section  being  formed 
of  a  single  plate  with  a  longitudinal  riveted  joint  and  the 
different  sections  being  riveted  together  by  transverse  joints. 
Small  steel  pipes  have  long  been  used  in  California  in  mining 
operations,  and  in  1876  one  of  36  inches  diameter  was  laid  at 
Rochester,  N.  Y. ;  since  1892  several  lines  of  larger  diameter 
have  been  constructed,  notably  the  East  Jersey  system  of  36, 
42,  and  48  inches  diameter,  and  a  line  at  Allegheny,  Pa.,  of 
60  inches  diameter.  On  the  Pacific  slope  wooden  pipes  are 


108  WATER-SUPPLY   SYSTEMS.  111. 

also  used ;  these  are  made  of  redwood  staves,  which  are  bound 
with  adjustable  steel  hoops. 

On  the  pipe  line  AB  there  should  be  a  valve  both  at  A  and 
at  B,  in  order  that  the  flow  may  be  regulated  or  be  entirely 
shut  off.  At  a  low  point  like  C  a  mud  valve  should  be  placed, 
in  order  to  clean  out  deposits  that  may  be  formed.  At  a 
high  point  like  D  an  air  valve  is  provided,  in  order  to  allow 
the  escape  of  the  air  which  collects  there.  The  line  AB, 
drawn  on  a  uniform  slope  from  the  water  level  in  A  to  that 
in  B,  is  called  the  hydraulic  grade  line.  No  point  of  the  pipe 
should  be  above  this  hydraulic  grade  line,  for  if  so  a  retarda- 
tion in  flow  is  liable  to  occur. 

When  the  valve  at  A  is  open  and  that  at  B  is  closed  the 
pressure  of  the  water  at  every  point  in  the  pipe  is  due  to  the 
head  of  the  water  level  in  A ;  thus  at  E  the  pressure  is  due 
to  the  head  EG  and  at  B  the  pressure  is  due  to  the  head  BH. 
When  the  valves  at  both  A  and  B  are  fully  open  the  condition 
of  things  is  very  different,  and  the  pressure  at  any  point  in 
the  pipe  is  due  to  the  head  measured  up  to  the  hydraulic 
grade  line;  thus  at  E  the  pressure  is  due  to  the  head  EF and 
at  B  the  pressure  is  that  due  to  the  depth  of  water  vertically 
above  the  end  of  the  pipe. 

The  method  of  the  last  article  may,  with  proper  modifica- 
tions, be  used  for  computing  the  flow  in  pipe  lines.  The 
length  /  is  here  the  length  of  the  pipe  measured  along  it  from 
A  to  B,  and  the  fall  h  is  the  difference  in  level  between  the 
water  surfaces  at  A  and  B  or  the  head  BH\  then  the  slope  s 
is  h/l.  If  the  diameter  of  the  pipe  is  d  the  area  of  its  cross- 
section  is  \nd*  and  its  circumference  is  nd\  hence  its  hydraulic 
radius  r  is  \d.  The  mean  velocity  of  flow  may  then  be 
written  v  =  c  ^dh/^l,  and  after  this  has  been  computed  the 
discharge  per  second,  q,  is  found  from  q  —  \nd*.v.  The 
coefficient  c  will,  as  before,  vary  with  the  roughness  of  the 
surface,  the  size  of  the  pipe,  and  the  slope  of  the  hydraulic 
grade  line. 


38. 


PIPE   LINES. 


109 


For  a  new  cast-iron  pipe,  coated  with  tar  or  asphalt,  the 
following  values  of  the  coefficient  c  may  be  used;  these,  like 
those  of  the  last  article,  are  derived  from  the  discussions  of 
Kutter.  For  an  old  pipe  the  values  of  r,  owing  to  incrusta- 
tions and  deposits,  may  be  20  or  30  per  cent  less  than  the 

COEFFICIENTS  FOR  CAST-IRON  PIPES. 


Diameter 
in  feet. 

J  =  O.OOOI 

S  =  O.OOO2 

s  =  0.0004 

J  =  O.OOI 

S  =  O.OI 

d=  0.5 

73 

79 

83 

87 

88 

d-\ 

92 

98 

102 

104 

106 

d=2 

112 

117 

120 

122 

124 

d=l 

124 

129 

131 

133 

134 

d=A 

132 

136 

138 

139 

141 

</=5 

140 

141 

142 

143 

144 

tabular  values.  For  a  steel  pipe,  owing  to  the  frictional 
resistance  of  the  rivets,  the  values  of  £,  and  hence  also  the 
velocity  and  discharge,  are  also  less  than  those  with  smooth 
inner  surfaces. 

As  an  example,  let  it  be  required  to  compute  the  discharge 
through  a  new  clean  pipe  30  inches  in  diameter  and  16400 
feet  long  under  a  head  of  49.2  feet.  Here  d=  2.5  feet, 
h  =  49.2  feet,  /  =  16  400  feet,  s  =  49.2/16  400  —  0.003,  and 
hence  from  the  table  c  =  128.  Then  by  computation  the 
mean  velocity  v  is  found  to  be  5-54  ^ee^  per  second,  and  the 
discharge  q  to  be  27.2  cubic  feet  per  second,  which  is  equiva- 
lent to  about  17  500000  gallons  per  day. 

The  inverse  problem,  to  find  the  diameter  of  a  pipe  to  carry 
a  given  discharge,  is  also  solved  by  the  use  of  the  above 
formulas  and  table.  For  example,  let  it  be  required  to  find 
the  diameter  to  carry  8  500  ooo  gallons  per  day  when  the 
length  of  the  pipe  is  25  400  feet  and  the  head  127  feet.  Here 
the  slope  s  is  0.005,  and  the  value  of  c  may  be  assumed  as 
IOO;  the  discharge  q  is  13.15  cubic  feet  per  second.  By 


IIO  WATER-SUPPLY   SYSTEMS.  III. 


transformation  the  above  formula  for  q  becomes  d  = 

from  which   the   diameter  d  is  found  to   be  0.89   feet;  this 

result  compared  with  the  table  shows  that  the  assumed  value 

of  c  is  not  far  from  correct  and  that  a  diameter  of  one  foot 

will  give  a  somewhat  greater  discharge  than  that  required. 

To  allow  for  all  contingencies  it  is  hence  well  to  use  a  12-inch 

pipe. 

While  the  above  gives  a  brief  outline  of  the  method  of 
designing  the  diameter  of  a  pipe  line,  it  should  be  said  that 
the  selection  of  the  proper  coefficient  is  a  matter  that  involves 
much  judgment  and  experience.  The  same  is  true  of  the 
location  of  the  route,  and  even  of  the  laying  of  the  pipe  in 
the  trenches.  The  thickness  of  the  pipe  will  be  different 
under  different  heads,  and  this  depends  also  upon  the 
diameter  and  the  kind  of  material;  in  Arts.  44  and  45  the 
question  of  thickness  is  further  discussed.  All  these  points 
require  careful  consideration  by  the  engineer,  in  order  that  the 
pipe  line  may  have  full  capacity,  an  ample  factor  of  safety, 
and  the  highest  degree  of  economy. 

39.  DISTRIBUTING  RESERVOIRS. 

A  distributing  reservoir  is  small  compared  with  a  storage 
reservoir,  as  the  latter  is  required  to  hold  sufficient  water  for 
two  or  three  months'  consumption,  while  the  former  is  to  pro- 
vide only  for  a  few  days.  Thus,  in  1897  the  city  of  New  York 
had  13  storage  reservoirs  with  a  capacity  of  38000000000 
gallons  and  5  distributing  reservoirs  with  a  capacity  of 
I  350000000  gallons.  In  times  of  heavy  rainfall  it  is  advis- 
able to  shut  off  the  connection  with  the  storage  reservoir,  in 
order  to  allow  time  for  sedimentation,  and  thus  in  general  it 
is  well  that  the  distributing  reservoirs  should  hold  a  supply 
sufficient  for  nearly  a  week.  A  large  city  has  several  dis- 
tributing reservoirs  for  the  supply  of  different  districts,  while 
a  small  town  has  perhaps  but  one.  Two  reservoirs  are  pref- 


39.  DISTRIBUTING   RESERVOIRS.  Ill 

erable  to  one,  however,  as  one  of  them  may  be  thrown  out 
of  use  while  the  other  is  undergoing  repairs  or  cleaning.  A 
connection  of  the  town  with  the  storage  reservoir  is  also 
always  advisable,  so  that  in  an  emergency  water  may  be  drawn 
directly  from  it. 

The  distributing  reservoirs  of  a  pumping  system  differ  in 
no  essential  respect  from  those  of  a  storage  system,  except 
that  they  should  usually  have  a  higher  capacity,  in  order  to 
allow  time  for  sedimentation.  Here  one  reservoir  is  decidedly 
inadvisable,  but  there  should  be  at  least  two,  one  of  which 
receives  the  water  from  the  pump  while  the  other  distributes 
it  to  the  town.  The  connection  between  the  two  reservoirs 
may  then  be  shut  off  for  a  day  or  two,  either  when  repairs 
are  necessary  or  when  the  water  pumped  is  turbid  owing  to 
river  floods.  Three  distributing  reservoirs  form  a  better 
arrangement  still.  For  example,  at  South  Bethlehem,  Pa., 
the  water  is  pumped  from  the  Lehigh  River  to  a  reservoir  of 
12  oooooo  gallons  capacity,  from  which  it  passes  to  two  smaller 
ones  having  a  combined  capacity  of  3000000  gallons;  here 
the  large  reservoir  acts  like  the  storage  reservoir  of  a  gravity 
system,  and  pumping  may  be  discontinued  for  several  days 
when  the  river  water  is  turbid,  while  at  the  same  time  either 
one  of  the  smaller  reservoirs  may  be  thrown  out  of  use  when- 
ever necessary. 

A  distributing  reservoir  is  built  upon  a  hill  which  has  suffi- 
cient elevation  to  give  the  required  pressure  throughout  the 
town.  A  storage  reservoir  made  by  damming  a  valley  requires 
no  excavation  further  than  that  of  removing  the  vegetable 
matter  in  the  top  layer  of  the  soil,  but  a  distributing  reservoir 
on  a  hill  involves  considerable  excavation.  The  most  eco- 
nomical location  is  generally  near  the  brow  of  the  hill,  where 
the  work  will  be  partly  excavation  and  partly  embankment,  as 
shown  in  the  figure.  Extraordinary  care  must  be  taken  that 
this  embankment  may  have  no  tendency  to  slide  and  that  no 
water  may  percolate  through  it.  The  shape  of  the  reservoir 


112  WATER-SUPPLY   SYSTEMS.  III. 

will  depend  upon  the  configuration  of  the  ground  and  the 
capacity  required.  The  depth  of  water  in  the  middle  usually 
ranges  from  15  to  30  feet. 

Most  distributing  reservoirs  require  to  be  lined  with  con- 
crete, in  order  to  prevent  leakage.  The  earth  over  the  entire 
inner  surface  should  be  thoroughly  rolled  and  then  a  layer  of 
about  one  foot  of  clay  is  applied  and  consolidated  by  tamp- 


SECTION  OF  A  DISTRIBUTING  RESERVOIR. 

ing.  Over  this  a  layer  of  concrete  is  placed,  the  thickness  of 
this  being  also  about  one  foot.  Sometimes  an  asphalt  lining 
is  added,  since  concrete  is  more  or  less  pervious  to  water 
under  a  head  of  20  or  30  feet. 

When  a  distributing  reservoir  is  filled  from  an  aqueduct  the 
regulation  of  the  entering  water  must  be  done  entirely  at  the 
storage  reservoir.  When  it  is  filled  from  a  pipe  line  there 
should  be  a  valve  at  both  reservoirs,  and  the  closing  of  one 
will  shut  off  the  supply.  If  both  valves  are  open  the  maxi- 
mum discharge  of  the  pipe  occurs,  but  the  energy  of  the  flow 
is  scarcely  sufficient  to  raise  the  water  a  foot  above  the  outlet 
end.  In  order  to  throw  the  entering  water  into  the  air,  so 
that  it  may  absorb  oxygen,  the  discharge  must  be  diminished 
by  putting  nozzles  on  the  outlet  end ;  this  increases  the  height 
of  the  hydrauMc  grade  line  throughout  and  gives  a  pressure 
head  which  will  cause  fountain  streams  to  rise. 

The  gate  chamber  at  the  distributing  reservoir  is  arranged 
in  a  manner  similar  to  that  at  the  storage  reservoir.  A  waste 
pipe  to  draw  off  the  water  is  laid  from  the  lowest  part  of  the 
bottom  to  a  convenient  point  of  discharge  beyond  the  em- 
bankment. All  distributing  reservoirs  should  be  cleaned  of 


4O.  PUMPS  AND  PUMPING.  11$ 

mud  deposits  once  a  year,  and  some  require  cleaning  at  shorter 
intervals.  It  has  occasionally  happened  that  a  reservoir  has 
become  polluted  with  sewage;  in  such  a  case  its  surface  must 
be  most  thoroughly  washed  with  sodium  hypochlorite  or 
calcium  chloride,  in  order  to  kill  all  the  bacteria. 

When  filter  beds  or  mechanical  filters  are  used  in  a  gravity 
system  these  are  generally  placed  between  two  reservoirs,  one 
of  which  receives  the  water  from  the  storage  reservoir  and 
delivers  it  to  the  filter  plant  while  the  other  receives  the  puri- 
fied water  and  distributes  it  to  the  town.  In  a  pumping 
system  with  distributing  reservoirs  a  similar  arrangement  may 
be  followed,  or  the  filter  plant  may  be  near  the  river  and  the 
purified  water  be  pumped  to  the  reservoir.  When  the  system 
of  pumping  to  a  tank  or  stand-pipe  is  employed  it  is  neces- 
sary that  the  filtering  should  be  done  before  the  water  passes 
through  the  pumps. 

40.  PUMPS  AND  PUMPING. 

For  raising  water  out  of  an  open  or  driven  well  a  suction 
pump  may  be  used  if  the  lift  is  not  over  30  feet.  For  a  higher 
lift  the  combined  suction  and  force  pump  must  be  used,  and 
this  must  be  placed  within  30  feet  of  the  water  level.  If  a 
perfect  vacuum  could  be  formed  it  would  be  possible  to  raise 
water  34  feet  by  suction,  but  in  practice,  on  account  of  leak- 
age in  valves,  this  limit  cannot  be  attained.  Through  the 
lift  above  the  pump  the  water  is  forced  up  by  the  pressure 
exerted  by  the  piston;  if  this  exerts  a  pressure  of  /  pounds 
per  square  inch  the  theoretic  height  of  lift  in  feet  is  2.3O4/, 
but  on  account  of  frictional  resistances  this  also  cannot  be 
attained. 

A  common  type  of  single-acting  pump  is  that  which  has  a 
horizontal  cylinder  and  a  solid  piston.  When  the  piston 
moves  through  the  stroke  from  C  to  D  the  upper  valve  closes 
and  the  lower  one  opens;  thus  a  partial  vacuum  is  formed  and 


114 


WATER-SUPPLY    SYSTEMS. 


III. 


the  atmospheric  pressure  causes  the  water  to  rise  from  A  and 
fill  the  cylinder.  When  the  piston  moves  through  the  stroke 
from  D  to  C  the  lower  valve  closes  and  the  upper  one  opens 
and  the  water  is  forced  up  through  the  discharge  pipe  to  the 
outlet  at  B.  The  effective  work  done  by  the  pump  is  that  of 
raising  the  water  through  the  distance  AB,  and  the  total  work 


A 


SINGLE-ACTING  PUMP. 

is  this  effective  work  plus  that  required  to  overcome  the  fric- 
tional  and  retarding  resistances. 

Two  single-acting  cylinders  placed  side  by  side  and  con- 
nected with  the  same  suction  pipe  and  discharge  pipe  are 
generally  called  a  duplex  pump.  The  pistons  move  in  oppo- 
site directions,  so  that  when  one  is  forcing  water  through  the 
discharge  pipe  the  other  is  drawing  water  up  the  vacuum  pipe. 
Three  cylinders  may  be  also  used,  in  which  case  it  is  called  a 
triplex  pump.  In  order  to  cause  a  uniform  flow  in  the  dis- 
charge pipe,  as  also  to  render  the  operation  more  smooth,  an 
air  vessel  is  generally  provided ;  into  this  the  flow  from  the 
pump  cylinders  passes  and  out  of  it  the  discharge  pipe  rises. 
The  air  in  the  vessel,  being  compressed  by  the  water  pressure, 
acts  like  a  cushion  to  absorb  shocks  and  the  flow  up  the  dis- 
charge pipe  becomes  perfectly  continuous. 

A  double-acting  pump  is  one  that  forces  the  water  in  both 
strokes  of  the  piston.  When  the  piston  moves  from  C  to  D 
the  valves  E  and  F  open,  while  e  and  /close,  and  the  flow  of 


40.  PUMPS   AND    PUMPING.  IJ$ 

water  is  in  the  direction  of  the  letters  AEFB.  When  the 
piston  moves  from  D  to  C  the  valves  e  and /open,  while  E 
and  F  close,  and  the  water  follows  the  direction  AefB.  Here, 
as  in  all  cases,  the  effective  work  of  the  pump  is  that  of  rais- 


I 

DOUBLE-ACTING  PUMP. 

ing  the  water  from  the  level  below  A  to  the  desired  elevation 
above  B. 

The  centrifugal  pump,  while  formerly  used  only  for  low 
lifts,  has  been  so  developed  in  recent  years  that  it  is  now  also 
used  for  very  high  lifts.  It  is  used  more  than  any  other  pump 
in  connection  with  water  purification  plants,  where,  however, 
the  lifts  are  usually  low.  Its  greatest  advantage  probably  lies 
in  the  fact  that  it  can  be  direct-connected  to  an  electric  motor, 
thereby  eliminating  losses  due  to  gears,  pulleys,  etc.,  and  at 
the  same  time  economizing  space.  As  a  general  proposition 
the  centrifugal  pump  is  cheaper,  both  in  first  cost  and  in 
operation,  than  any  type  of  plunger  pump. 

The  air  lift  pump  is  an  apparatus  for  increasing  the  flow  of 
deep  wells  by  forcing  compressed  air  through  a  pipe  a  con- 
siderable distance  below  the  ordinary  water  level.  The  mix- 
ture of  air  and  water  is  lighter  than  water  alone  and  hence 
rises  to  a  greater  height.  Water,  50  feet  or  more  below  the 


Il6  WATER-SUPPLY   SYSTEMS.  III. 

surface  of  the  ground,  may  be  raised  to  that  surface  in  this 
manner. 

The  capacity  of  a  pump  is  measured  by  the  greatest  amount 
of  water  it  can  deliver  per  day;  thus  a  pump  of  3000000 
gallons  capacity  is  understood  to  be  one  that  can  raise 
3  ooo  ooo  gallons  of  water  in  24  hours.  This  gives,  however, 
little  idea  of  the  work  done  by  the  pump  unless  the  height  of 
lift  or  the  pressure  that  it  maintains  is  also  stated.  A  pump 
of  3  ooo  ooo  gallons  capacity  lifting  water  through  a  height 
of  100  feet  becomes  merely  one  of  I  500  ooo  gallons  capacity 
if  the  height  of  lift  is  200  feet. 

The  power  of  a  pump  is  the  number  of  horse-powers  it  can 
deliver,  and  one  horse-power  is  the  performance  of  550  foot- 
pounds of  work  in  one  second.  Thus,  if  I  200  ooo  gallons  of 
water  is  to  be  raised  through  a  height  of  230  feet  in  24  hours 
the  weight  to  be  lifted  in  one  second  is  n6J  pounds  and  the 
power  required  is  48.6  horse-powers.  The  effective  power  of 
the  pump  must,  however,  be  considerably  higher  than  this,  as 
work  is  lost  in  overcoming  the  frictional  resistances  due  to  the 
flow  in  the  pipe  as  well  as  in  the  pump  cylinders. 

Pumps  are  driven  by  steam,  water-power,  wind,  electric 
motor  or  gas  engine,  the  two  latter  coming  into  more  and  more 
use  in  late  -years.  When  steam  is  used  with  reciprocating 
pumps  the  steam  cylinders  and  water  cylinders  are  direct-con- 
nected and  this  arrangement  is  known  as -a  pumping  engine. 

41.    PUMPING  ENGINES. 

A  pumping  engine  is  one  run  by  steam,  the  pumps,  steam 
cylinders,  and  boilers  forming  one  plant  which  must  be  con- 
sidered as  a  whole  in  discussing  its  economy,  since  the  coal 
burned  under  the  boilers  is  a  large  item  in  the  operating  ex- 
penses. Such  a  plant  should  not  only  have  a  horse-power 
sufficient  to  deliver  the  required  quantity  of  water  under  the 
given  pressure,  but  the  cost  of  installation  and  operation  should 


41.  PUMPING  ENGINES.  1 1/ 

be  such  as  to  be  most  economical.  A  cheap  pumping  engine 
will  consume  more  coal  than  an  expensive  one,  just  as  a  cheap 
coat  will  require  more  repairs  than  one  of  higher  price.  The 
amount  of  coal  consumed  annually  is  therefore  as  important 
an  item  to  be  considered  as  that  of  the  first  cost  of  the  pump- 
ing plant. 

The  duty  of  a  pumping  engine  is  the  number  of  foot- 
pounds of  work  that  it  can  do  with  an  expenditure  of  100 
pounds  of  coal.  This  is  the  old  definition  of  duty,  as  first 
stated  by  Watt,  and  it  is  still  very  useful  in  general  discus- 
sions. Thus,  when  it  is  said  that  a  pumping  engine  has  a 
duty  of  120  ooo  ooo  it  is  meant  that  120  ooo  ooo  foot-pounds 
of  work  can  be  performed  by  it  by  burning  100  pounds  of 
coal  under  the  boilers.  The  ambiguity  in  this  definition 
regarding  the  meaning  of  the  word  coal  has,  however,  led  to 
a  more  precise  definition,  but  the  old  definition  will  agree  with 
the  modern  one  if  the  coal  be  understood  to  be  of  such 
quality  that  one  pound  of  it  is  capable  of  generating  10000 
British  heat  units,  or  7  780  ooo  foot-pounds  of  work. 

The  steam  engine  is  a  very  wasteful  utilizer  of  the  energy 
in  coal.  Nearly  one-half  of  this  energy  goes  up  the  chimney, 
and  about  one-third  is  lost  in  the  exhaust  steam,  so  that  more 
than  one-fifth  of  it  is  rarely  utilized.  A  pumping  engine  of 
150000000  duty  utilizes  19.3  per  cent,  one  of  100000000 
duty  utilizes  12.9  per  cent,  and  one  of  50000000  duty 
utilizes  only  6.4  per  cent.  The  higher  the  duty  the  greater 
is  the  amount  of  work  that  can  be  done  with  one  pound  of 
coal.  Using  coal  of  the  standard  quality,  as  above  defined, 
100  pounds  burned  in  one  hour  produces  75.8  horse-powers 
with  a  150000  ooo-duty  engine,  50.5  horse-powers  with  a 
I oo  ooo  ooo- duty  engine,  and  25.2  horse-powers  with  a 
50  ooo  ooo-duty  engine.  Or,  if  1000  pounds  of  coal  are 
required  to  do  a  given  amount  of  work  with  a  150  ooo  ooo- 
duty  engine  1500  pounds  will  be  required  with  a  100  ooo  ooo- 
duty  engine  and  3000  pounds  with  a  50  ooo  ooo-duty  engine. 


WATE.R-SUPPLY   SYSTEMS. 


III. 


A  high-duty  engine  is  an  expensive  one  and  a  low-duty 
engine  is  a  cheap  one.  In  any  particular  case  the  question 
of  consumption  will  determine  the  required  capacity,  and  this 
together  with  the  pressure  will  determine  the  horse-power. 
It  is  then  necessary  to  go  into  the  market  and  ascertain  the 
prices  of  pumping  engines  of  different  duties  to  do  the  work 
required.  The  cost  and  calorific  power  of  the  coal  to  be  used 
are  also  to  be  ascertained.  Then  the  prices  of  installation  are 
discussed  in  connection  with  the  costs  of  operation,  and  thus 
the  most  economical  engine  may  be  selected.  If  coal  is  very 
dear  a  high-duty  engine  is  best;  if  coal  is  very  cheap  an 
engine  of  low  duty  will  be  preferable. 

For  example,  take  a  town  whose  mean  daily  consumption 
of  water  is  2  500  ooo  gallons  per  day,  which  is  to  be  delivered 
into  the  pipes  under  a  pressure  of  50  pounds  per  square  inch 
at  the  pump,  while  the  suction  height  is  5  feet.  Here  50 
pounds  per  square  inch  is  equivalent  to  a  head  of  1 15  feet,  so 
that  the  work  required  is  the  same  as  if  the  supply  were  lifted 
through  a  height  of  120  feet.  The  capacity  of  this  pumping 
engine  should  be  at  least  5  ooo  ooo  gallons  per  day  in  order 
to  meet  the  demands  of  the  Monday  consumption,  and 
accordingly  the  maximum  work  to  be  done  is  5  013  ooo  ooo 
foot-pounds  per  day,  and  the  effective  power  required  is 
closely  1 06  horse-powers.  On  obtaining  prices  or  bids  for 
COMPARISON  OF  ECONOMY  OF  PUMPING  ENGINES. 


Duty. 

Millions  of 
foot-pounds. 

Cost  of 
Pumping 
Engine. 

Annual  interest 
and  sinking  fund 
at  7  per  cent. 

Annual  cost 
of  coal  at 
$3  per  ton. 

Annual  payment 
for  interest 
and  coal. 

150 
140 

$24000 
20000 

$1680 
1400 

$817 
876 

$2497 
2276 

130 

I70OO 

IIQO 

942 

2132 

120 
110 

I5OOO 
14000 

1050 
980 

1022 
III4 

2072 
2094 

100 
QO 

13000 
12  OOO 

910 
840 

1225 
1362 

2135 
2202 

41.  PUMPING   ENGINES.  119 

pumping  engines  of  this  capacity  and  power  it  is  found  that 
the  cost  of  those  of  different  duties  are  as  given  in  the  second 
column  of  the  table.  If  the  annual  interest  on  this  cost, 
together  with  a  contribution  to  a  sinking  fund  in  order  to 
repay  the  principal  after  a  certain  number  of  years,  be  7  per 
cent  the  annual  expense  for  this  purpose  is  given  in  the  third 
column.  Now  as  the  mean  consumption  is  2  500  ooo  gallons 
per  day  under  a  head  of  120  feet,  the  mean  work  per  day  is 
2  506  ooo  ooo  foot-pounds,  and  100  times  this,  divided  by  the 
duty,  gives  the  number  of  pounds  of  coal  used  per  day; 
whence,  for  coal  at  $3  per  gross  ton,  the  annual  cost  of  coal 
is  found  and  recorded  in  the  fourth  column.  The  sum  of  the 
annual  interest  charge  and  annual  cost  of  coal  gives  the  last 
column  of  the  table,  from  which  it  is  concluded  that  the 
120  ooo  ooo-duty  pumping  engine,  whose  cost  is  $15  ooo,  is 
the  most  economical. 

It  is  here  very  clearly  seen,  as  in  so  many  other  cases  in  the 
preceding  articles,  that  expert  knowledge  is  necessary  in  order 
to  purchase  a  pumping  engine  and  secure  the  highest  degree 
of  economy.  Of  course  anyone  can  buy  a  pump,  but  only 
the  experienced  engineer  is  able  to  buy  one  which  will  be  just 
suited  to  do  the  required  work,  and  which  at  the  same  time 
will  give  the  highest  degree  of  economy.  To  insure  that  the 
pumping  engine  installed  conforms  to  the  specifications  under 
which  it  is  bought,  a  test  must  be  made  before  paying  for  it. 
This  test  will  determine  the  calorific  capacity  of  the  coal,  the 
indicated  horse-power  of  the  steam  cylinders,  the  capacity 
of  the  pump  working  under  the  assigned  pressure,  the 
efficiency  of  the  steam  and  water  machinery,  and  the  duty  of 
the  combined  plant.  If  the  results  of  such  a  test  show  that 
the  apparatus  does  not  meet  the  requirements  of  the  specifi- 
cations it  is  clear  that  a  claim  for  reduction  in  the  stipulated 
price  should  be  made,  or  that  such  alterations  should  be 
demanded  as  will  cause  the  plant  to  fulfil  those  requirements. 


120  WATER-SUPPLY  SYSTEMS.  III. 

42.  PUMPING  TO  RESERVOIRS. 

Pumping  systems  of  water  supply  are  of  two  classes,  one 
having  a  distributing  reservoir  where  sedimentation  may 
occur,  and  the  other  having  none.  The  first  class  will  here 
be  described.  As  far  as  the  distributing  reservoir  is  concerned 
the  remarks  in  Art.  39  explain  the  general  method  of  con- 
struction. The  water  from  the  pump  enters  the  reservoir  by 
one  pipe,  while  other  pipes  distribute  it  either  to  other  reser- 
voirs or  to  the  town.  Thus  in  the  following  figure  CB 
represents  the  pipe  leading  from  the  pump  C  to  the  reservoir 
B,  while  BD  is  the  pipe  which  carries  the  water  out  of  the 
reservoir. 

A  river  is  the  most  common  source  of  supply,  and  a  well 
should  be  excavated  in  or  near  its  bank  for  the  reception  of 
the  suction  pipe.  Such  a  well  is  usually  lined  with  rubble 


H 
PUMPING  FROM  RIVER  TO  RESERVOIR. 

masonry  without  cement,  so  that  the  water  may  enter  through 
the  walls  as  well  as  through  the  bottom,  and  it  is  covered  so 
that  the  refuse  of  floods  may  not  enter  at  the  top.  In  some 
cases  the  well  is  built  below  the  river  bottom  instead  of  on 
the  bank,  and  in  other  cases  it  is  built  on  the  river  bottom 
and  the  water  admitted  through  iron  gratings. 

The  pump  C  must  be  located  so  that  the  vertical  height  of 
the  pump  cylinders  above  the  water  in  the  well  is  less  than  30 
feet  and  preferably  less  than  20  feet.  The  vertical  height  of 
the  reservoir  B  above  the  pump  is  not  often  greater  than  300 
feet  and  usually  less  than  250  feet.  The  location  of  the 


42. 


PUMPING  TO    RESERVOIRS. 


121 


reservoir  with  respect  to  the  pump  and  the  town  depends,  of 
course,  on  the  topography  of  the  region,  and  this  will  deter- 
mine the  lengths  of  the  force  and  distribution  pipes. 

The  power  of  the  pump  must  be  sufficient  to  lift  the  water 
through  the  height  /i,  which  is  the  same  as  G£,  or  the  differ- 
ence in  level  between  the  water  surfaces  in  the  well  and  reser- 
voir, and  also  to  overcome  the  frictional  resistances.  Of  these 
resistances  the  most  important  is  that  of  the  friction  of  the 
water  in  the  pipe;  this  increases  with  the  square  of  the 
velocity  of  flow,  and  hence  may  be  made  small  by  using  a 
pipe  of  large  diameter.  In  the  figure  the  line  CE  represents 
the  pressure-head  at  C  when  there  is  no  motion  of  water  in 
the  pipe  CB,  and  CF  represents  the  pressure-head  when  the 
pump  is  at  work;  thus  EF  is  the  head  which  is  required  to 
overcome  the  friction  in  the  force  pipe.  In  like  manner  the 
apparent  height  of  lift  for  the  suction  pipe  is  CG,  but  on 
account  of  friction  this  is  increased  to  CH.  Thus  the  pump 
must  have  an  effective  power  sufficient  to  overcome  the  total 
head  between  H  and  F,  as  well  as  the  resistances  due  to  its 
pistons  and  valves. 

It  is  shown  in  treatises  on  hydraulics  that  the  friction-head 
caused  by  the  mean  velocity  v  in  a  pipe  of  length  /  and 
diameter  d  depends  upon  the  roughness  of  the  inner  surface 
of  the  pipe,  its  diameter,  and  the  mean  velocity  of  flow.  The 
following  table  gives  values  of  this  friction-head  for  100  feet 
FRICTION-HEAD  FOR  100  FEET  OF  PIPE. 


Diameter 
in   feet. 

V  =   I 

V  =  2 

z>  =  3 

v  =  4 

p  =  6 

V  =   10 

0.25 

0.20 

O.7O 

1.46 

2.40 

5-37 

0.5 

0.09 

0.32 

O.7O 

I.I4 

2.46 

6.22 

0-75 

0.05 

0.21 

0.45 

0.73 

1-57 

3-94 

I 

0.04 

0.15 

0.32 

0-55 

1.  12 

2.80 

1-5 

0.02 

0.09 

0.20 

0-33 

0.67 

1.66 

2 

0.06 

0.13 

0.21 

0-45 

1.09 

122  WATER-SUPPLY   SYSTEMS.  III. 

in  length  of  clean  cast-iron  pipe,  and  from  it  the  friction-head 
for  any  other  length  is  readily  obtained.  The  values  of  v  at 
the  tops  of  the  columns  are  in  feet  per  second.  For  example, 
if  a  pipe  12  inches  in  diameter  and  12  570  feet  long  discharges 
52  850  gallons  per  hour  the  mean  velocity  in  feet  per  second 
is  v  =  2.5  and  the  table  gives  0.235  feet  as  the  friction-head 
for  100  feet  of  pipe;  whence  the  friction-head  for  the  given 
pipe  is  125.7  X  0.235  =  29.5  feet.  If  the  height  of  lift  is 
120  feet  the  pump  must  hence  be  able  to  overcome  the  pres- 
sure due  to  a  head  of  149.5  feet. 

As  an  illustration  of  the  effect  of  the  size  of  the  pipe  on  the 
horse-power  of  the  pump  suppose  that  500  ooo  gallons  per 
hour  is  required  to  be  raised  through  a  vertical  height  of  230 
feet  from  the  well  A  to  the  reservoir  B,  the  total  length  of 
the  pipe  being  4200  feet.  Here  the  discharge  per  second 
through  the  pipe  is  1.86  cubic  feet,  or  closely  116  pounds, 
and  the  power  required  to  lift  this  through  230  feet  is  48.2 
horse-powers.  If  the  pipe  be  6  inches  in  diameter  the  mean 
velocity  is  9.47  feet  per  second  and,  from  the  table,  the  fric- 
tion-head is  about  233  feet,  or  more  than  the  given  lift,  so  that 
the  pump  would  have  to  exert  about  97  horse-powers.  If  the 
pipe  be  12  inches  in  diameter  the  mean  velocity  is  2.37  feet 
per  second,  the  table  gives  8.9  feet  as  the  friction-head,  and 
50.2  horse-power  is  required.  The  great  advantage  of  using 
a  large  pipe  is  here  plainly  shown,  and  in  any  given  case  such 
a  size  is  to  be  selected  as  will  render  a  minimum  the  total 
annual  expenses,  both  for  interest  and  operation,  of  the  entire 
pumping  system. 

43.  DIRECT  PUMPING. 

The  second  class  of  pumping  systems  is  that  where  the 
pump  delivers  the  water  directly  into  the  main  which  supplies 
the  town.  This  class  has  three  subdivisions:  first,  where  a 
part  of  the  water  goes  to  a  tank  which  holds  a  supply  sufficient 


43.  DIRECT  PUMPING.  123 

to  allow  the  pump  to  stop  for  a  day  or  several  hours;  second, 
where  a  stand  pipe  is  placed  near  the  pump  which  holds  a 
supply  sufficient  to  allow  a  stoppage  of  an  hour  or  two;  third, 
where  no  tank  or  stand  pipe  is  used,  so  that  the  supply  of  the 
town  is  entirely  dependent  upon  the  pressure  exerted  by  the 
pump  pistons. 

The  method  of  pumping  to  a  tank  is  illustrated  in  the  fol- 
lowing figure,  where  A  is  the  pump  well,  C  the  pump,  and 


PUMPING  WITH  TANK. 

CB  the  pipe  running  to  the  tank  and  through  the  town,  where 
lateral  pipes,  marked  Z>,  carry  the  water  into  different  streets. 
If  there  be  no  water  taken  from  the  pipe  between  C  and  B, 
and  a  distribution  pipe  K  delivers  it  out  of  the  tank  B,  the 
system  is  the  same  as  that  described  in  the  last  article.  In 
many  cases  the  water  is  delivered  both  out  of  the  main  pipe 
and  out  of  the  tank,  thus  making  a  mixed  system.  As  far  as 
pumping  capacity  and  power  are  concerned  there  is  little 
difference  between  the  two  classes.  In  each  GE  is  the  height 
of  lift  and  HF  is  the  total  effective  head  that  the  pump  must 
overcome. 

The  method  of  pumping  with  a  stand  pipe,  illustrated  in 
the  next  figure,  consists  in  forcing  the  water  into  the  stand 
pipe  PE  until  it  is  nearly  filled.  The  head  PE  then  produces 
the  necessary  pressure  to  cause  the  distribution  through  the 
mains.  The  best  location  for  the  stand  pipe  is  near  the 
pump,  as  it  then  acts  somewhat  like  an  air  vessel  to  neutralize 
the  effect  of  shocks,  the  water  rising  in  it  when  the  flow  is 
suddenly  checked  instead  of  bringing  a  direct  shock  on  the 


124  WATER-SUPPLY  SYSTEMS.  III. 

pump  cylinders.  Here,  as  before,  EF  represents  the  head 
which  measures  the  frictional  resistances  in  the  street  mains 
beyond  P.  If  the  pump  stops  the  water  level  at  E  immedi- 


PUMPING  WITH  STAND  PIPE. 

ately  falls  with  the  consumption,  and  after  a  short  time  the 
pressure  in  the  street  mains  is  materially  lowered. 

The  method  of  direct  pumping  without  the  use  of  tank  or 
stand  pipe  may  be  illustrated  by  omitting  the  tank  in  the  first 
of  the  above  figures;  here  the  pump  must  maintain  a  pressure 
corresponding  to  the  head  CF,  of  which  EF  is  expended  in 
overcoming  the  friction  in  the  mains.  If  the  stand  pipe  in 
the  second  figure  be  omitted  it  also  represents  the  method. 
The  regulation  of  the  pumping  engine  in  this  method  is 
effected  through  the  water  pressure  itself  by  means  of  a 
weighted  vertical  piston  or  some  other  suitable  device. 
When  no  water  is  being  drawn  in  the  town  the  pump  is 
motionless;  when  a  little  is  drawn  it  moves  slowly  to  keep  up 
the  supply  and  pressure;  when  the  draft  is  heavy  it  moves 
rapidly.  Whatever  be  the  consumption  the  regulation  should 
be  such  as  to  maintain  in  the  pipes  a  pressure  equivalent  to 
the  head  below  the  horizontal  line  BE.  It  is  seen  that  dupli- 
cate pumping  engines  are  almost  indispensable,  for  if  there  be 
only  one  a  stoppage  for  repairs  deprives  the  entire  town  of 
its  supply. 

The  computation  of  the  power  of  the  pumping  engine 
required  to  furnish  the  maximum  hourly  consumption  is  the 
same  for  these  three  methods  and  differs  from  that  of  the  last 


43-  DIRECT   PUMPING.  12$ 

article  only  in  regard  to  the  friction-head,  which  is  generally 
not  so  great,  since  the  velocity  of  the  water  in  the  mains 
decreases  with  the  distance  from  the  pump.  The  head  CE 
will  be  determined  by  the  pressure  which  is  to  be  maintained; 
if  100  pounds  per  square  inch  is  required,  then  this  head  is 
230  feet.  The  given  consumption  and  the  size  of  the  pipes 
at  C  or  P  determine  the  mean  velocity  at  that  point,  and  from 
this,  by  the  help  of  the  table  of  the  last  article,  a  value  of  the 
friction-head  is  found.  One-half  or  one-third  of  this  will,  in 
general,  be  all  that  is  really  expended  in  days  of  ordinary 
draft,  but  if  a  fire  occurs  the  flow  may  be  so  concentrated  in 
certain  mains  that  the  full  value  of  the  computed  friction-head 
is  reached.  It  is,  therefore,  probably  best  to  take  it  as  given 
by  the  table  in  cases  of  design,  but  in  the  investigation  of  an 
existing  system  a  detailed  investigation  will  be  necessary  to 
determine  an  accurate  value.  If  the  street  mains  are  large 
the  head  lost  in  friction  will  be  small,  but  if  mains  of  small 
diameter  be  used  the  friction  may  become  so  great  as  to 
require  an  engine  of  high  power  whose  coal  consumption  may 
be  a  serious  item  of  expense. 

The  method  of  direct  pumping  with  or  without  a  stand  pipe 
is  adapted  to  towns  on  level  ground,  and  is  extensively  used 
in  the  prairie  regions  of  the  central  states.  Chicago  in  1897 
had  about  30  pumping  engines  at  seven  different  stations 
which  delivered  the  water  of  Lake  Michigan  throughout  the 
city,  the  total  capacity  of  the  pumps  being  358  ooo  ooo  gallons 
per  day;  one  of  these  engines  pumped  to  a  reservoir  of  small 
capacity,  and  at  two  stations  there  were  stand  pipes  138  and 
167  feet  in  height;  thus  the  greater  part  of  the  service  is  by 
the  third  method  of  direct  delivery.  Where  the  topography 
admits,  the  method  of  pumping  to  tanks  or  that  of  pumping 
to  distributing  reservoirs  is  generally  preferred  on  account  of 
the  advantage  of  maintaining  even  a  small  amount  of  storage 
for  cases  of  emergency.  There  is,  of  course,  nothing  in  any 
system  which  renders  it  universally  more  advantageous  or 


126  WATER-SUPPLY   SYSTEMS.  Ill, 

economical  than  another,  but  the  engineer,  in  each  particular 
case,  selects  that  system  or  combination  of  systems  which  the 
local  conditions  will  render  the  most  reliable  and  at  the  same 
time  give  the  lowest  annual  outlay  for  the  interest  on  con- 
struction and  the  expenses  of  operation. 

44.  TANKS  AND  STAND  PIPES. 

A  tank  may  be  built  of  masonry,  the  cross-section  being 
rectangular  and  the  side  walls  of  sufficient  thickness  to  safely 
withstand  the  lateral  pressure  of  the  water.  Such  a  construc- 
tion is,  however,  too  expensive  when  the  depth  of  water  is 
over  10  or  15  feet,  on  account  of  the  very  thick  walls  that  are 
required.  For  greater  heights  the  common  method  is  to 
build  a  structure  of  circular  cross-section  with  wrought-iron  or 
steel  plates  riveted  together  like  a  large  steel  water  pipe. 
It  is  connected  to  the  masonry  foundation  by  steel  angles  or 
knees,  and  all  the  joints  and  connections  must  of  course  be 
water-tight.  The  top  is  usually  left  open,  but  it  is  best  to 
put  a  roof  over  it  in  order  to  prevent  the  multiplication  of 
algae  under  the  action  of  sunlight,  and  in  very  cold  regions 
the  tank  should  be  entirely  housed  with  wood  or  brick  in 
order  to  decrease  the  liability  to  freezing. 

The  height  of  a  tank  depends  upon  the  pressure  that  is  to 
be  maintained  in  the  town  and  the  elevation  of  the  hill  on 
which  it  stands,  and  its  diameter  depends  upon  the  quantity 
of  storage  that  is  required.  Tanks  larger  than  50  feet  in 
diameter  and  60  feet  high  are  not  common ;  one  of  this  size 
will  hold  about  880  ooo  gallons,  and  if  all  of  this  is  available 
for  consumption  it  is  sufficient  for  one  day's  supply  for  a  town 
of  9000  people.  A  tank  of  smaller  diameter  may  be  built 
higher  than  60  feet,  since  the  thickness  of  the  steel  plates 
decreases  with  the  diameter;  thus  a  tank  might  be  30  feet  in 
diameter  and  100  feet  high,  and  its  capacity  would  be  about 
490  ooo  gallons. 


44. 


TANKS  AND   STAND   PIPES. 


127 


A  stand  pipe  may  be  built  of  steel  plates  exactly  like  a  tank, 
but  its  diameter  is  less  and  its  height  usually  greater.  The 
tallest  stand  pipes  are  about  250  feet  in  height,  but  the  num- 
ber higher  than  200  feet  is  small.  As  the  function  of  a 


STAND  PIPES. 

stand  pipe  is  to  preserve  pressure  rather  than  to  maintain 
storage,  it  is  clear  that  height  is  an  element  of  greater  impor- 
tance than  diameter.  The  water  in  the  lower  portion  of  the 
stand  pipe  is,  moreover,  not  available  for  storage,  since  the 
water  level  cannot  fall  to  the  base  without  causing  all  pressure 
to  vanish.  Hence  the  form  of  construction  shown  in  the 
right-hand  diagram  of  the  figure  is  frequently  adopted;  here 
a  trestle  tower  is  built,  on  which  the  stand  pipe  CD  is  erected, 
and  the  water  is  carried  to  it  by  a  vertical  pipe  BC  rising  from 
the  main  AB.  The  pressure  produced  at  B  by  the  head  BD 
is  the  same  in  the  two  cases,  but  in  the  second  one  only  the 
water  in  CD  is  available  for  storage. 

The  thickness  of  the  plates  of  a  tank  or  stand  pipe  generally 
increases  from  the  top  toward  the  base,  since  the  higher 
pressure  requires  the  greater  amount  of  metal  to  resist  it. 
The  computation  of  thickness  is  exactly  like  that  of  a  water 
main  under  a  given  head.  If  h  be  the  head  in  feet  the  pressure 
in  pounds  per  square  inch  is/  =  0.434/2.  Then,  as  shown  in 


128  WATER-SUPPLY   SYSTEMS.  III. 

treatises  on  applied  mechanics,  the  equation  2St  —  /^applies 
to  all  questions  of  longitudinal  strength.  Here  d  is  the 
diameter  of  the  pipe  and  /  the  thickness  of  the  metal,  both  in 
inches,  and  5  is  the  tensile  stress  per  square  inch  produced  in 
the  metal  by  the  water  pressure.  For  cast  iron  a  safe  value 
of  6"  is  about  2000  pounds  per  square  inch;  for  a  pipe  of 
medium  steel  whose  joints  have  an  efficiency  of  70  per  cent 
a  safe  value  of  5  is  9000  pounds  per  square  inch.  Thus  in 
the  figure  if  the  head  BD  on  the  base  of  the  steel  stand  pipe 
be  80  feet  and  its  diameter  20  feet  the  thickness  of  the  plates 
should  be  \  inch,  while  at  the  mid-height  the  thickness  need 
be  only  one-half  as  great.  For  the  second  diagram  if  the 
cast-iron  pipe  BC  is  18  inches  in  diameter  a  thickness  of 
•J  inch  is  theoretically  sufficient  to  withstand  the  pressure, 
but  cast-iron  pipes  must  be  made  thicker  than  this  on  account 
of  the  stresses  to  which  they  are  subject  in  transportation  and 
handling.  Tanks  and  stand  pipes  also  receive  stresses  from 
the  action  of  the  wind  and  these  must  be  carefully  taken  into 
account  in  the  design. 

Several  failures  of  tanks  and  stand  pipes  due  to  the  action 
of  wind,  to  the  accumulation  of  ice  near  the  top,  and  to 
defective  material  or  workmanship  have  occurred.  The 
effect  of  a  gale  of  wind  on  an  empty  stand  pipe  is  often  more 
injurious  than  on  one  that  is  filled  with  water;  as  additional 
security  against  wind  tall  stand  pipes  are  frequently  provided 
with  guys  of  steel  rope.  A  thick  layer  of  ice  at  the  top,  fall- 
ing after  the  water  level  has  been  drawn  down,  has  been  the 
cause  of  failures.  One  of  the  tallest  stand  pipes  ever  erected 
was  that  at  Gravesend,  H.  Y. ;  this  was  250  feet  high,  16  feet 
in  diameter  at  the  base,  and  8  feet  in  diameter  at  the  top;  at 
the  first  trial,  when  the  water  had  reached  the  height  of  227 
feet,  a  crack  occurred  near  the  base  and  an  instant  later  the 
entire  structure  fell  with  a  deluge  of  water. 

Stand  pipes  proper  placed  near  the  pumping  engine  are 
not  now  built  as  extensively  as  formerly,  since  the  method  of 


45-  STREET   MAINS   AND   FIRE   SERVICE,,  1 29 

pumping  directly  into  the  pipes  has  been  so  developed  that 
reliable  regulation  of  the  supply  can  be  assured;  the  method 
of  using  a  trestle  base  has  increased  in  favor,  and  in  some 
cases  a  wooden  construction  with  iron  hoops  is  employed. 
Large  metallic  tanks  are  extensively  built  on  masonry  and 
concrete  foundations  in  order  to  obtain  storage  sufficient  to 
allow  stoppage  of  the  pumps  for  a  few  hours.  The  height  of 
water  in  the  tank  is  known  at  the  engine  house  either  by 
readings  of  the  water  gage  or  preferably  by  an  electric  device 
operated  by  a  float  in  the  tank.  A  manhole  is  provided  near 
the  base  of  the  tank,  so  that  access  may  be  had  to  it  without 
climbing  over  the  top  when  repairing  or  cleaning  is  to  be  done. 

i 
45.  STREET  MAINS  AND  FIRE  SERVICE. 

The  first  street  mains  used  in  the  United  States  were  made 
of  logs,  through  each  of  which  a  hole  2  or  3  inches  in  diameter 
was  bored,  and  these  were  connected  with  an  end  mortise-and- 
tenon  joint.  Cast-iron  pipes  were  next  used,  and  these  are 
now  more  extensively  employed  than  any  other  kind.  Steel- 
riveted  pipes  cannot  economically  compete  with  cast-iron  ones 
except  for  the  large  sizes  required  in  conduit  lines.  Wooden 
pipes  made  of  staves  and  bound  with  steel  hoops  have  been 
used  for  street  mains  only  in  a  few  towns. 

Cast-iron  pipes  are  made  of  different  thickness,  depending 
on  the  diameter  and  the  head  under  which  they  are  to  be  used. 
For  instance,  pipes  6  inches  in  diameter  have  thicknesses  of 
0.41  and  0.45  inches  for  heads  of  100  and  200  feet  respec- 
tively, while  pipes  12  inches  in  diameter  have  thicknesses  of 
0.53  and  0.60  inches,  and  pipes  24  inches  in  diameter  have 
thicknesses  of  0.76  and  0.90  inches  for  the  same  heads.  They 
are  cast  in  lengths  of  12  feet,  each  having  a  spigot  end  and 
a  bell  end.  When  laid  in  the  trench  the  spigot  end  of  one 
length  is  inserted  into  the  bell  end  of  the  next  length,  a 
gasket  is  forced  into  the  annulus  to  the  proper  depth,  and 


130  WATER-SUPPLY   SYSTEMS.  III. 

melted  lead  is  poured  in  to  fill  the  joint.  Whenever  a  change 
in  diameter  is  required  this  is  made  by  a  special  tapering 
length  called  a  reducer.  Special  lengths  shorter  than  12  feet 
are  also  provided  for  curves,  for  points  where  branch  pipes  are 
to  connect,  and  for  places  where  stop  valves  are  to  be  inserted. 

Hydrants  are  usually  placed  at  street  corners;  in  towns  the 
post  hydrant  is  most  common,  while  the  flush  hydrant  is  used 
in  cities,  as  the  latter  form  does  not  project  above  the  pave- 
ment. In  the  northern  states  a  frost  casing  is  necessary  to 
prevent  freezing.  The  connection  of  the  hydrant  to  the  main 
ought  to  be  by  a  pipe  not  less  than  six  inches  in  diameter  in 
order  that  the  pressure  in  the  main  may  not  be  lost  by  the 
friction  of  the  flowing  water.  The  valve  that  closes  the 
hydrant  should  move  slowly  in  order  to  prevent  the  water 
ram  that  occurs  under  a  sudden  closure. 

When  a  high  pressure  exists  at  the  hydrants  two  or  three 
lines  of  fire  hose  may  be  attached  to  one,  and  thus  streams 
may  be  thrown  without  the  help  of  fire  engines.  If  the  pres- 
sure at  the  hydrants  be  80  pounds  per  square  inch  or  more  it 
may  be  called  high  pressure.  When  one  line  of  best  hose, 
50  feet  long  and  having  a  I -inch  smooth  nozzle,  is  attached 
to  a  hydrant  where  the  pressure  is  80  pounds  per  square  inch 
the  discharge  at  the  nozzle  will  be  about  245  gallons  per 
minute  and  the  height  to  which  the  stream  will  rise  for  effec- 
tive work  will  be  about  85  feet,  although  some  of  the  water 
will  rise  to  130  feet.  If  two  or  three  lines  of  hose  be  attached 
the  discharge  of  each  and  the  effective  heights  of  the  streams 
will  be  much  lower,  since  the  increased  draft  will  cause  a 
decrease  in  pressure  at  the  hydrant. 

The  following  figures,  derived  from  the  experiments  of 
Freeman,  show  the  results  that  may  be  expected  from  differ- 
ent hydrant  pressures  by  the  use  of  100  feet  of  ordinary  best 
quality  rubber-lined  hose  with  a  i-inch  smooth  nozzle 
attached : 


45-  STREET   MAINS   AND   FIRE   SERVICE.  131 

Pressure  in  pounds  per  square  inch  20     40     60     80     100 

Discharge  in  gallons  per  minute  117   167   205   236     263 

Vertical  height  of  stream  in  feet  27     52     72     82       89 

Horizontal  range  of  stream  in  feet  31     48     60     70       76 

The  heights  and  ranges  here  given  are  those  at  which  the 
jet  will  be  a  good  effective  fire  stream  when  a  moderate  wind 
is  blowing,  the  extreme  drops  going  considerably  further. 
With  common  hose  these  distances  will  be  somewhat  de- 
creased; and,  of  course,  the  longer  the  hose  the  less  will  be 
the  discharge  and  height  of  the  stream.  The  great  value  of 
pressure  in  fire  service  is  very  plainly  shown  by  these  figures, 
and  a  town  which  has  a  gravity  supply  with  high  pressure 
enjoys  a  good  protection  without  the  expense  of  maintaining 
fire  engines. 

High  pressure,  however,  like  many  other  good  things,  has 
some  disadvantages.  One  is  that  it  requires  the  street  mains 
and  house-pipes  to  be  of  greater  thickness,  and  hence  more 
costly,  than  under  a  medium  pressure.  Another  is  that  it 
increases  the  consumption,  for  the  greater  the  pressure  the 
greater  becomes  the  waste  due  to  leakage  and  to  carelessness 
of  consumers.  When  part  of  a  town  is  on  a  hill  the  mainte- 
nance of  a  high  pressure  there  involves  an  excessive  pressure  in 
other  parts  unless  some  method  of  reducing  it  is  employed* 
and  for  this  purpose  pressure  regulators  are  often  used. 

A  pressure  regulator  is  an  apparatus  inserted  in  a  pipe  line 
which  reduces  the  pressure  in  the  pipes  below  it  to  such  a 
limit  as  may  be  desired.     The  principle 
of  its  action  will  be   understood  from 
the  figure,  where  A  represents  a  pipe  in 
which  the  pressure  is  100  pounds  per 
square    inch.     This   pipe   runs   into   a 
chamber  where  the  pressure  acts  against 
a    piston    loaded    with    a    weight     W.       PRESSURE  REGULATOR. 
This  weight  is  sufficient  to  cause  a  pressure  of  40  pounds  per 
square  inch  on  the  lower  side  of  the  piston,  and  hencr  the 


132  WATER-SUPPLY  SYSTEMS.  III. 

pressure  in  the  pipe  B  cannot  exceed  60  pounds  per  square 
inch.  If  water  be  drawn  out  anywhere  along  this  pipe  B  the 
pressure  in  it  falls  below  60  pounds  per  square  inch,  and  hence 
the  piston  rises  and  water  flows  from  A  into  B  until  the  pres- 
sure is  restored.  By  varying  the  weight  W  the  difference  of 
the  pressures  in  the  two  parts  of  the  chambers  may  be  regu- 
lated at  pleasure.  Instead  of  a  weight  a  spring  is  generally 
used,  or  sometimes  a  weighted  lever. 

When  the  direct  system  of  pumping  is  employed  the  regu- 
lation of  the  pressure  within  certain  limits  may  be  made  at  the 
engine  house.  During  the  night  it  may  be  lowered  in  order 
to  prevent  waste,  and  it  may  be  quickly  increased  to  the 
maximum  limit  by  the  man  in  charge  when  a  fire  breaks  out 
in  the  town.  In  order  that  no  failure  in  this  program  may 
occur  it  is  necessary  that  an  emergency  should  always  be 
anticipated  #nd  that  constant  and  vigilant  foresight  should  be 
exercised  to  meet  it. 

46.  WATER  METERS  AND  HOUSE-PIPES. 

The  measurement  of  the  daily  consumption  of  a  town  is 
effected  in  a  gravity  system  by  noting  the  water  levels  in  the 
distributing  reservoirs  at  times  when  there  is  no  flow  into 
them ;  these  levels  together  with  known  areas  of  the  water 
surfaces  enable  the  volume  taken  out  of  the  reservoirs  to  be 
computed.  In  a  pumping  system  the  consumption  is  deter- 
mined from  the  displacement  of  the  pump  cylinders  and  the 
number  of  strokes.  There  is  also  an  apparatus,  known  as  the 
Venturi  water  meter,  which  may  be  placed  in  a  pipe  line  and 
which  will  make  a  continuous  record  showing  the  consumption 
.during  every  minute,  hour,  and  day. 

Water  meters  for  the  measurement  of  the  consumption  in 
factories  and  hotels  are  frequently  used,  and  the  system  is  in 
some  cities  also  applied  to  many  dwellings,  as  it  is  found  that 
the  waste  of  water  is  thereby  much  lessened.  Commonly  a 


46.  WATER   METERS   AND   HOUSE-PIPES.  133 

consumer  pays  by  the  year,  but  in  the  meter  system  he  pays 
by  the  gallon  and  accordingly  faucets  are  not  left  open  unless 
it  is  necessary.  Wherever  meters  have  been  introduced  it  has 
been  found  that  a  marked  decrease  in  consumption  has 
resulted.  For  example,  at  Hoboken,  N.  J.,  in  1883  there 
were  2700  taps,  of  which  47  had  meters,  and  the  mean  daily 
consumption  was  121  gallons  per  person;  in  1888  there  were 
5600  taps,  of  which  2667  had  meters,  and  the  mean  daily 
consumption  had  fallen  to  55  gallons  per  person. 

A  house  water  meter  is,  like  a  gas  meter,  provided  with  dials 
which  register  the  consumption  in  cubic  feet  or  gallons.  The 
pointers  on  these  dials  are  attached  to  wheels  and  these  are 
turned  by  parts  of  the  apparatus  which  move  when  water 
flows  through.  The  piston  meter  is  one  of  the  most  reliable 
kinds,  and  in  this  the  motion  of  water  causes  two  pistons  to 
move  in  opposite  directions,  the  water  entering  and  leaving 
the  cylinders  by  slide  valves  somewhat  similar  to  those  in  a 
steam  engine.  The  rotary  meter  has  a  wheel  incased  so  that 
it  is  caused  to  move  by  the  water  passing  through.  The  screw 
meter  has  a  helical  surface  which  revolves  on  its  axis  as  the 
water  enters  at  one  end  and  passes  out  at  the  other.  The 
disk  meter  has  a  wabbling  disk  so  incased  that  its  motion  is 
proportional  to  the  volume  of  water  passing  through.  All 
meters  require  to  be  tested  before  being  put  into  use,  so  that 
the  error  of  registration,  if  any,  may  be  known. 

The  house  supply  is  brought  from  the  main  by  a  wrought- 
iron  pipe  usually  I  inch  in  interior  diameter,  but  the  connec- 
tion to  the  main  is  generally  made  by  a  tap  not  greater  than 
j  inch  in  diameter.  This  tap  is  inserted  by  the  water  com- 
pany, but  the  consumer  lays  the  pipe  into  the  cellar  of  his 
house,  where  it  passes  through  the  meter,  when  one  is  used, 
and  then  branches  to  the  laundry,  the  kitchen,  and  the  bath- 
room. All  these  branch  pipes  should  be  of  wrought  iron,  for 
lead  pipes  sometimes  act  unfavorably  upon  the  water  and 
holes  may  be  eaten  in  them  by  rats.  The  pipes  should  be 


134  WATER-SUPPLY    SYSTEMS.  III. 

everywhere  visible,  except  when  it  is  necessary  to  run  them 
horizontally  under  a  floor,  in  order  that  ready  access  to  them 
may  be  had  whenever  alterations  or  extensions  are  needed. 
They  may  be  bronzed  or  galvanized  in  the  kitchen  and  bath- 
room, or  for  these  rooms  brass  pipes  may  be  used  by  those 
who  can  afford  the  increased  expense. 

In  the  kitchen  the  water  is  carried  into  a  vertical  hollow 
cylinder  called  a  boiler,  and  from  the  bottom  of  this  a  pipe 
runs  through  the  water-back  in  the  range  and  back  again. 
The  hot  water  from  the  range  rises  to  the  top  of  the  boiler, 
whence  the  hot-water  pipes  run  to  the  laundry,  the  kitchen 
sink,  and  the  bath-room.  Whenever  hot  water  is  drawn  cold 
water  enters  the  boiler,  sinks  to  the  bottom,  and  circulates 
back  again  through  the  range. 

Each  water  closet  is  provided  with  a  flush  tank  which  is 
supplied  from  a  cold-water  pipe ;  when  the  tank  is  discharged 
a  float  falls  and  opens  a  valve  in  the  pipe,  and  when  the  tank 
is  again  filled  the  valve  is  closed  by  the  rising  float. 

For  a  house  of  ten  or  twelve  rooms  there  are  in  the  laundry 
about  six  faucets,  three  for  cold  and  three  for  hot  water 
The  kitchen  sink,  the  bath-tub,  and  two  wash-stands  have 
four  faucets  for  cold  water  and  four  for  hot  water.  Two 
water  closets  have  two  cold-water  connections.  All  these 
fixtures  are  provided  with  overflows,  so  that  the  water  cannot 
rise  above  a  certain  height.  For  this  water  the  householder 
pays  from  $10  to  $15  per  year  and  may  use  and  waste  as  little 
or  as  much  as  he  desires.  On  the  meter  plan  he  pays  from  10 
to  15  cents  per  thousand  gallons.  For  a  family  of  ten  persons 
and  the  generous  daily  allowance  of  50  gallons  per  person  the 
meter  plan  will  generally  be  more  economical  than  that  of 
yearly  payment. 

The  water-works  are  now  completed  and  the  supply  is 
brought  into  the  houses.  The  collecting  reservoir  has  im- 
pounded the  run-off  and  delivered  it  to  the  distributing  basins, 


47-  EXERCISES  AND   PROBLEMS.  135 

or  the  pumps  have  raised  the  river  water  from  a  well  at  the 
bank.  The  quality  of  the  water  has  been  improved  by  aera- 
tion, sedimentation,  and  natural  filtration,  or  if  of  suspicious 
quality  it  has  been  purified  either  by  artificial  filtration  or  by 
mechanical  methods.  An  abundant  supply  under  ample  press- 
ure fills  the  street  mains,  giving  full  security  against  fire,  and 
allowing  all  street  pavements  to  receive  thorough  cleaning. 
Fountains  rise  in  the  public  park,  and  every  lawn  is  kept 
green  in  the  time  of  drought.  The  faucets  are  openeJ  in  the 
houses,  and  out  of  them  comes  pure  and  sparkling  water  whose 
use  brings  strength  and  health  to  the  family.  The  first  part 
of  the  construction  work  of  the  sanitary  engineer  is  done. 
But  the  clear  and  pure  water  is  rendered  immediately  im- 
pure by  its  use,  and  hence  the  second  part  of  his  work  is  to 
follow,  whereby  the  foul  water  or  sewage  is  to  be  removed 
from  the  town  in  such  manner  as  to  still  further  promote  the 
health  of  the  community. 


47.  EXERCISES  AND  PROBLEMS. 

31.  Consult  Baker's   Manual  of  American  Water  Works  for  1897, 
and   compare   five  or  six  cities  with  respect  to  population,  kind  of 
system,  daily  consumption,  and  method  of  filtration.     See  Flynn's 
statistics  in  Engineering  News,  July  7,  1898. 

32.  What  pressure  in  pounds  per  square  inch  is  produced  by  a 
static  head  of  230  feet  of  water  ? 

33  (a)  A  reservoir  is  full  on  July  i,  receives  600000  gallons  per 
day  during  July,  400  ooo  during  August,  and  200000  during  Sep- 
tember. What  should  be  its  capacity  in  order  to  furnish  a  town 
with  a  supply  of  700  ooo  gallons  per  day  during  these  three  months 
and  yet  be  one-third  full  at  the  end  of  September? 

33  (b)  Solve  the  same  problem,  taking  the  mean  area  of  the  water 
surface  as  2.85  acres  and  supposing  that  the  evaporation  during  the 
three  months  from  this  surface  is  o.i  inches  per  day. 

34  (a)  An  earthen  dam  has  a  width  of  18  feet  on  top,  a  front  slope 
of  i£  to  i,  and  a  back  slope  of  2  to  i.     How  many  cubic  yards  of 


136  WATER-SUPPLY  SYSTEMS.  III. 

material  are  required  for  a  height  of  36  feet  and  a  length  of   100 
feet  ?  how  many  for  a  height  of  24  feet  and  a  length  of  100  feet  ? 

34  (b)  The  South  Fork  dam  near  Johnstown,  Pa.,  had  an  area  of 
407.4  acres  at  the  ordinary  height  of  water  and  456.8  acres  when 
the  water  level  was  5  feet  higher.  The  mean  discharge  of  the  waste- 
weir  while  the  water  was  rising  through  this  5  feet  was  about  1000 
cubic  feet  per  second.  If  the  rainfall  was  0.8  inches  per  hour  and 
one-half  of  this  reached  the  reservoir,  how  many  hours  were  required 
to  cause  the  rise  of  5  feet  ? 

34  (c)  Consult  the  novel  "  Put  Yourself  in  His  Place,"  by  Charles 
Reade,   and    give    his  description  of  the    breaking  of  the    dam  of 
Dale  Dyke   reservoir  near  Sheffield,  England,  in   1861.     Ascertain 
the  main  dimensions  of  this  dam  and  the  cause  of  its  failure. 

35  (a)  A  masonry  dam  36  feet  high  has  a  vertical  back,  its  top 
thickness  is  y-J-  feet,  and  its  cross-section  is  a  trapezoid.     Compute 
the  proper  base  thickness. 

35  (b)  A  masonry  dam  of  trapezoidal  cross-section  is  60  feet  high, 
its  top  thickness  is  9  feet,  its  base  thickness  is  30  feet,  and  the  bat- 
ter of  the  back  is  2  inches  per  foot.  Find  where  the  resultant 
pressure  Fis  applied  on  the  base  of  the  wall,  and  state  whether  the 
dam  has  the  proper  degree  of  security. 

35  W  Consult  Schuyler's  monograph  on  Reservoirs  for  Irrigation, 
in  Report  of  U.  S.  Geological  Survey  for  1896-97,  and  describe  the 
construction  of  rock-fill  dams.     Describe  also  the  Bear  Valley  dam 
and  the  Sweetwater  dam. 

36  (a)  A  watershed  of  2.64  square  miles  furnishes  water  to  a  res- 
ervoir whose  area  is  3.25  acres.     If  a  rainfall  of  one  inch  per  hour 
occurs  and  one-half  of  this  reaches  the  reservoir  in  one  hour,  what 
should  be  the  width  of  the  waste-weir  if  its  sill  is  4.5  feet  below  the 
top  of  the  dam  ? 

36  (b)  Consult  Transactions  of  American  Society  of  Civil  En- 
gineers for  1891,  Vol.  XXIV,  pp.  431-469,  and  give  further  par- 
ticulars regarding  the  failure  of  the  South  Fork  dam. 

37.  Consult  Report  of  the  Aqueduct  Commissioners  of  New  York 
City  for  1887-1895;  give  an  account  of  some  defects  in  construc- 
tion of  the  new  Croton  Aqueduct  due  to  inefficient  inspecion, 
and  explain  how  these  defects  were  remedied. 

38  (a)  A  pipe  line  represented  by  the  figure  is  23  700  feet  long 
and  its  inner  diameter  is  12  inches.  The  elevations  of  the  water 


47-  EXERCISES  AND   PROBLEMS.  137 

levels  A  and  B  above  tide-water  are  694.3  and  587.3  feet,  and  that 
of  the  point  £is  597.5  feet;  the  distance  along  the  pipe  line  from  E 
to  B  is  10  350  feet.  Find  the  prescure  in  pounds  per  square  inch 
at  E  when  the  valve  at  A  is  open  and  that  at  B  is  closed.  Find  the 
pressure  when  both  valves  are  open. 

38  (b)  Compute  the  diameter  required  to  deliver  6  ooo  ooo  gallons 
per  day  through  a  pipe  18  320  feet  long  with  a  total  fall  of  13  feet. 

39  (a)  A  distributing  reservoir  about  15  feet  deep  has  an  area  of 
20  574  square  feet  at  the  highest  water  level,  16  175  square  feet  at  5 
feet   and    10  440    square  feet    at  10  feet    below   that  level.     How 
many  gallons  are  contained  in  the  upper  10  feet  of  the  reservoir  ? 

39  (b)  Consult  Folwell's  Water-supply  Engineering  (New  York, 
1917),  or  Turneaure  and  Russell's  Public  Water-supplies  (New  York, 
1916).  Obtain  sketches  showing  the  arrangement  of  embankments 
and  gate  chambers  for  distributing  reservoirs. 

40.  If  the  water  gage  at  a  pump  reads  65  pounds  per  square 
inch,  and  250  ooo  gallons  of  water  are  pumped  in  one  hour  with 
a  suction  lift  of  6  feet,  what  is  the  effective  horse-power  of  the 
pump  ? 

41  (a)  Visit  a  pumping  engine  and  describe  the  boilers,  steam 
cylinders,  and  water  cylinders  ;  ascertain  steam  and  water  pressures, 
height  of  suction  lift,  and  capacity  of  the  pumps. 

41  (b)  A  pumping  engine  is  to  be  purchased  to  deliver  a  mean 
daily  consumption  of  4  ooo  ooo  gallons,  and  the  total  lift,  includ- 
ing frictional  losses,  is  72  feet.  Taking  the  prices  of  engines  of 
different  duties  as  10  per  cent  greater  than  those  given  in  the 
table  of  Art.  41,  and  coal  at  $4  per  ton,  determine  which  engine 
is  the  most  economical  ? 

42.  In  the  figure   the  pipe  AC  is  180  feet  long  and   18  inches 
in  diameter,  while  CB  is  1800  feet  long  and  12  inches  in  diameter. 
If  the  total  height  of  lift  from  A  to  B  is  105  feet,   what  horse- 
power is  required  to  pump  150  ooo  gallons  per  hour? 

43.  Collect  data  regarding  the  water' supply  of  Indianapolis,  Ind., 
St.  Louis,  Mo.,  New  Orleans,  La.,  and  other  cities. 

44  (a)  Consult  the  articles  by  Pence  in  Engineering  News,  1894, 
and  describe  the  failures  of  the  stand  pipes  at  East  Providence, 
R.  L,  Peoria,  111.,  and  Thomasville,  Ga. 

44  (b)  A  steel  stand  pipe  180  feet  high  and  12  feet  in  diameter 
has  plates  £  inch  thick  at  the  base.  What  is  its  factor  of  safety  ? 


138  WATER-SUPPLY   SYSTEMS.  III. 

44  (c)  Visit  a  steel  tank  or  stand  pipe,  take  its  dimensions,  and 
make  drawings  of  the  horizontal  and  vertical  riveted  joints.     Ex- 
plain why  the  rivets  are  differently  arranged  in  these  joints. 

45  (a)  Collect  sketches  showing  the  arrangement  and  operation 
of  the  valves  in  different  kinds  of  hydrants. 

45  (&)  What  are  the  theoretic  heights  to  which  a  stream  will  rise 
under  pressures  of  40  and  80  pounds  per  square  inch  ? 

46  (a)  Collect  sketches  showing  the  arrangement  and  operation 
of  the  Crown  meter,  the  Thomson  meter,  and    the  Worthington 
meter. 

46  (t>)  Make  a  vertical  section  of  a  kitchen  boiler  and  show  how 
the  water  circulates  in  it. 

47  (a)  What  is  electrolysis    in    water    mains  ?     What  is  the  dis- 
tinction between  a  ring  nozzle  and  a  smooth  nozzle  ?     What  is  the 
derivation  of  the  word  Plumber  ?     Explain  the  action  of  an  auto- 
matic flush  tank  for  a  water  closet. 

47  (b)  A  water  company  is  assured  that,  by  extending  its  mains 
to  a  neighboring  village,  400  taps  may  be  obtained,  each  yielding 
$7  per  annum.  If  money  can  be  borrowed  at  5  per  cent  per  an- 
num, and  a  sinking  fund  at  3.5  per  cent  compound  interest  be 
established  to  repay  it  in  12  years,  what  sum  is  the  company  justi- 
fied in  expending  in  order  to  earn  during  those  12  years  a  net 
income  of  $200  per  year  ? 

47  (c)  Consult  Transactions  of  American  Society  of  Civil  Engineers 
for  1912  and  obtain  data  regarding  the  Morena  rock-fill  dam  at  San 
Diego,  California. 

47  (d)  Consult  engineering  periodicals  and  obtain  sketches  of  some  of 
the  hollow  reinforced  concrete  dams  recently  constructed. 


48.  HISTORICAL   NOTES. 


CHAPTER  IV. 
SEWERAGE    SYSTEMS. 

48.  HISTORICAL  NOTES. 

The  organic  wastes  of  a  household  are  of  two  kinds,  garbage 
and  sewage.  Garbage  is  the  solid  refuse  of  kitchens,  such  as 
vegetables,  pieces  of  meat,  and  bones.  Sewage  is  the  liquid 
refuse  of  the  laundry,  kitchen,  and  bath-room,  and  consists 
of  water  fouled  with  soap,  vegetable  and  animal  matter,  urine 
and  faeces. 

The  ancient  methods  of  disposing  of  these  household 
wastes,  and  the  methods  which  are  still  followed  by  the  larger 
part  of  mankind,  were  to  throw  them  out  upon  the  ground  to 
evaporate  and  act  as  manure,  to  bury  them  in  the  ground,  to 
cast  them  into  a  stream,  or  to  consume  them  by  fire.  Earth, 
air,  water,  and  fire  are  the  four  natural  deodorizers  and  puri- 
fiers of  decaying  organic  matter.  Air  and  water  furnish 
oxygen,  which  enables  the  bacteria  to  perform  their  useful 
work  of  decomposing  such  matter  into  harmless  constituents; 
earth  acts  in  connection  with  air  to  produce  the  purification 
of  liquid  wastes  in  the  same  manner  in  which  water  is  purified 
by  filtration;  fire  directly  oxidizes  or  consumes  both  the 
decaying  garbage  and  the  noxious  bacteria  which  accompany 
it.  Indeed  all  modern  methods  for  the  disposal  of  garbage 
and  sewage  depend  upon  the  scientific  application  of  these 
properties  of  earth,  air,  water,  and  fire. 

Savage  and  barbarous  man  throws  his  refuse  into  a  pile  near 
his  tent  or  hut,  and  when  the  collection  becomes  so  large  as 


140  SEWERAGE   SYSTEMS.  IV. 

to  cause  offense  and  disease  he  moves  his  dwelling  to  a  new 
location.  Civilized  man  removes  the  refuse  at  once  from  the 
vicinity  of  his  dwelling  and  thus  keeps  the  air  and  soil  around 
him  free  from  pollution. 

A  sewerage  system  is  a  plant  for  the  removal  of  sewage 
from  a  town.  The  water-supply  system  brings  to  the  town 
pure  water,  the  sewerage  system  carries  away  the  same  water 
fouled  with  household  wastes.  The  pure  water  enters  the 
town  through  a  single  pipe  line,  which  branches  into  the  street 
mains,  and  these  again  branch  into  the  house-pipes.  The  foul 
water  or  sewage  leaves  the  houses  through  small  drains  con- 
necting with  larger  ones  in  the  streets,  and  these  unite  into 
one  large  sewer  which  conveys  the  sewage  to  a  safe  distance 
from  the  town.  A  sewerage  system  hence  requires  a  water- 
supply  system  for  its  successful  operation. 

Damascus,  the  oldest  city  of  the  world,  and  regarded  by 
the  ancients  as  the  fairest  of  earthly  paradises,  has  always  had 
an  abundant  supply  of  pure  water  from  the  river  Abana,  which 
also  carries  away  the  refuse  from  both  streets  and  dwellings. 
At  Nineveh  and  Jerusalem  arched  drains  or  sewers  were  built 
in  early  times.  At  Rome  a  great  sewer  called  Cloaca  maxima 
was  built  in  558  B.C.  to  drain  the  valley  of  the  Forum;  this 
sewer  was  32  feet  in  height  and  about  500  linear  feet  of  it  are 
still  in  service.  Later  Rome  also  built  many  sewers  to  carry 
away  the  water  furnished  by  its  extensive  system  of  aque- 
ducts, so  that  Pliny  speaks  of  it  as  a  city  on  arches. 

These  ancient  sewers,  like  many  modern  ones,  served  for 
two  purposes:  first,  to  carry  away  the  rainfall  and  the  run-off 
of  brooks;  and  second,  to  carry  away  the  foul  water  or  sewage 
proper.  An  underground  conduit  which  is  built  merely  for 
the  first  purpose  is  generally  called  a  drain;  when  sewage  is 
admitted  into  it  the  word  sewer  should  be  used.  A  drain  is 
usually  of  rude  construction,  often  made  by  walling  in  and 
arching  over  a  brook;  a  sewer,  however,  must  be  water-tight, 


48.  HISTORICAL  NOTES.  14! 

so  that  the  soil  may  not  be  polluted  by  leakage.  London 
had  drains  during  the  seventeenth  and  eighteenth  centuries, 
but  no  household  refuse  except  liquid  kitchen  slops  was 
allowed  to  enter  them  until  1815.  The  real  sewe'rrge  system 
of  London  dates  from  1847,  when  the  drains  had  been  so  im- 
proved and  extended  that  it  was  made  compulsory  to  turn  all 
sewage  into  them. 

Prior  to  1850  the  methods  for  removing  the  sewage  of 
towns  and  cities  were  generally  the  same  as  those  still  in  use 
in  villages  and  country  districts,  namely,  kitchen  sewage  was 
run  into  the  streets  and  fields  to  evaporate  or  percolate  into 
the  ground,  while  the  sewage  of  privies  and  water  closets  was 
run  into  vaults  and  cesspools  either  to  soak  into  the  soil  or  to 
be  removed  at  stated  intervals.  Both  the  privy  vault  and  the 
cesspool  were  intended  to  allow  the  sewage  to  remain  upon 
the  premises  as  long  as  possible,  and  they  were  emptied  only 
when  the  offense  became  great.  As  a  consequence  the  soil 
of  towns  and  cities  was  fouled,  wells  were  polluted,  and 
epidemics  of  disease  were  caused.  By  the  use  of  water-tight 
vaults  and  cesspools,  which  are  emptied  only  in  cold  weather, 
this  system  may  be  made  a  good  one  in  country  districts,  but 
in  large  towns  and  cities  it  has  proved  to  be  impracticable 
from  a  sanitary  point  of  view. 

A  pail  system  for  the  removal  of  the  refuse  of  privies  and 
water  closets  was  in  use  in  a  number  of  European  cities  at  the 
beginning  of  the  nineteenth  century  and  is  still  employed  to 
a  slight  extent.  This  system  consists  in  placing  pails  or  tubs 
beneath  the  seats  of  privies  and  removing  them  at  weekly 
intervals,  both  the  vessel  and  its  contents  being  taken  away 
and  replaced  by  a  clean  vessel.  Although  it  might  be 
thought  that  this  method  is  an  improvement  over  the  privy- 
vault  or  cesspool  system,  the  facts  show  that  the  offense 
caused  by  the  weekly  removal  of  the  material  is  so  great  that 
no  American  town  or  city  would  tolerate  it.  The  earth 
closet,  introduced  about  1865,  was  a  modification  of  the  pail 


142  SEWERAGE   SYSTEMS.  IV. 

system  in  which  the  vessel  was  partially  filled  with  dry  earth, 
and  more  added  from  day  to  day  until  it  became  full;  then  it 
was  carried  away  and  the  contents  used  on  the  fields  as 
manure.  This  method  also  proved  impracticable  on  a  large 
scale  by  reason  of  the  trouble,  offense,  and  expense  which  its 
operation  involved. 

The  water-carriage  method  of  the  ancient  Romans  has 
proved  to  be  the  only  practicable  and  economical  one  for  the 
removal  of  the  sewage  of  large  towns  and  cities.  This 
method,  since  its  development  in  London  and  Paris,  has 
rapidly  spread  over  Europe  and  America.  As  previously 
remarked,  a  water  supply  is  indispensable  for  its  operation. 
In  the  United  States  there  were  in  .1898  about  4000  towns 
and  cities  having  a  good  water  supply,  but  probably  not  one- 
fourth  of  these  had  an  efficient  sewerage  system.  The  reason 
for  this  lies  in  the  fact  that  a  water-works  brings  a  direct 
financial  return,  while  a  sewerage  plant  apparently  does  not. 
Private  companies  will  build  and  operate  a  water  supply  for  a 
town  and  secure  a  revenue  that  yields  a  good  profit  on  the 
investment,  but  the  construction  of  a  sewerage  system  must 
be  done  by  the  municipality,  and  the  average  taxpayer  sees 
only  the  expense  and  is  not  able  to  appreciate  its  benefits. 
These  benefits,  as  set  forth  in  the  first  chapter,  are  really 
nearly  equal  to  those  of  the  water  supply,  but  often  they  are 
only  fully  appreciated  when  unclean  streets  and  cesspool 
pollution  produce  an  epidemic  of  disease.  Such  object-lessons 
have  been  so  numerous  that  the  more  intelligent  citizens  of 
all  large  towns  generally  recognize  the  advantages  of  sewerage 
and  advocate  its  introduction.  The  work  now  done  by  boards 
of  health  in  investigating  the  causes  of  epidemics  and  in 
suggesting  methods  for  their  prevention,  is  exerting  a  most 
important  influence  upon  the  public  at  large.  Undoubtedly 
long  before  the  close  of  the  twentieth  century  every  town 
which  has  a  water  supply  will  be  provided  also  with  efficient 
sewerage. 


49- 


HOUSE  FIXTURES. 


49.  HOUSE  FIXTURES. 

About  one  per  cent  of  the  pure  and  abundant  water  supply 
which  enters  the  house  is  used  for  drinking  and  for  the  prep- 
aration of  food.  The  remainder  falls  into  the  laundry  tubs, 
the  kitchen  sink,  the  wash-stands,  the  bath-tub,  and  the  water 
closet,  whence  it  immediately  runs  away  as  sewage.  All 
these  fixtures  should  be  arranged  to  secure  perfect  cleanliness; 
they  should  not  be  boxed  in  with  woodwork,  but  every  part 
be  left  exposed  to  view,  so  that  there  may  be  no  place  around 
them  where  thoughtless  servants  can  conceal  sweepings  or 
dirty  rags. 

Each  of  these  fixtures  must  be  provided  with  a  trap,  so 
that  a  seal  of  water  may  be  preserved  in  its  outflow  pipe. 
This  is  necessary  because  the  main  soil  pipe  of  the  house 
sometimes  becomes  filled  with  foul  gas  from  the  decaying 
sewage,  which  would  rise  into  the  rooms  through  the  outflow 
pipes  were  it  not  for  the  water  seal  of  the  trap.  Of  the  many 
kinds  of  traps  only  four  will  be  mentioned.  The  bell  trap, 


BELL  TRAP. 


D  TRAP. 


S  TRAP. 


BALL  TRAP. 


sometimes  used  in  sinks,  has  a  bell  attached  to  the  strainer  to 
prevent  the  rise  of  gases;  this  is  an  objectionable  trap  because 
the  space  around  the  bell  is  so  large  as  to  collect  solid  matter, 
and  moreover  its  efficiency  is  entirely  destroyed  whenever  the 
strainer  is  removed.  The  D  trap  is  a  better  arrangement  for 
a  sink,  and  the  S  trap  is  better  still.  The  last  sketch  shows 
one  of  the  so-called  mechanical  traps  where  a  rubber  ball  is 


144  SEWERAGE   SYSTEMS.  IV* 

held  by  the  pressure  of  the  water  against  the  end  of  the  inlet 
pipe;  other  mechanical  traps  use  valves  or  floats  for  the  same 
purpose.  There  are  also  traps  in  which  a  mercury  seal  is 
used,  arrangement  being  made  that  the  water  cannot  force 
out  the  mercury. 

A  good  trap  is  one  constructed  so  that  it  will  be  thoroughly 
scoured  by  the  water  passing  through  it,  so  that  evaporation 
cannot  occur  and  so  that  syphonage  cannot  take  place.  The 
term  syphonage  is  used  to  designate  the  emptying  of  the  trap; 
thus  if  water  moves  slowly  through  the  S  trap  the  water  level 
will  remain  as  shown  in  the  figure,  but  if  a  large  quantity  is 
discharged  the  velocity  causes  a  negative  pressure,  so  that  the 
atmosphere  acting  down  the  inlet  pipe  forces  all  the  water  out 
of  the  trap.  To  prevent  syphonage  a  vent  pipe,  shown  by 
broken  lines,  is  inserted  on  the  sewer  side  of  the  trap  and  this 
runs  to  an  open  vent  tube;  by  this  arrangement  the  atmos- 
pheric pressure  acts  on  the  water  in  both  sides  of  the  trap. 
It  is  an  advantage  of  some  of  the  mechanical  traps  that 
syphonage  cannot  occur,  and  hence  that  vent  pipes  and  tubes 
are  unnecessary.  It  is  desirable  that  every  trap  should  be  so 
arranged  that  it  can  be  drained  and  its  interior  be  inspected 
by  the  plumber. 

The  laundry  tubs  discharge  soap  and  the  kitchen  sink  dis- 
charges both  soap  and  grease,  which  are  liable  to  clog  the  main 
soil  pipe.  In  hotels  and  large  houses  this  evil  becomes  so 
great  that  a  special  device,  called  a  grease  trap,  is  generally 
used.  This  is  a  box  placed  below  the  main  trap  and  having 
a  cover  which  can  be  easily  taken  off.  The  inlet  pipe  enters 
near  the  top,  and  the  outlet  pipe  is  a  syphon  rising  from  the 
bottom,  and  thus  the  soap  and  grease  are  left  to  float  on  the 
surface  of  the  water,  whence  they  are  removed  once  a  week. 

Every  laundry  tub,  sink,  wash-stand,  and  bath-tub  must  be 
provided  with  an  overflow  pipe,  and  it  is  important  that  this 
should  join  the  outlet  pipe  above  and  not  below  the  trap,  for 


49-  HOUSE   FIXTURES.  145 

otherwise  the  gas  will  rise  into  the  room  through  the  overflow 
pipe.  It  often  happens  that  plumbers,  in  order  to  effect  a 
straight  connection,  will  make  such  an  improper  junction.  If 
possible  all  traps  should  be  above  the  floor,  where  they  are 
easy  of  access,  and  by  a  little  careful  planning  on  the  part  of 
the  plumber  this  can  generally  be  done.  These  overflow 
pipes,  like  the  discharge  pipes  of  the  fixtures,  are  commonly 
of  lead,  with  wiped  joints. 

The  oldest  style  of  water  closet,  called  the  pan  closet,  had 
a  pan  operated  by  a  lever,  and  the  contents  of  the  pan  were 
dumped  into  a  bowl  beneath,  which  soon  became  foul  and 
offensive;  happily  this  dangerous  form  has  now  gone  out  of 
use.  Later  the  plunger  closet,  the  wash-out  closet,  and  the 
hopper  closet  were  introduced,  and  of  each  of  these  there  are 


PLUNGER  CLOSET.  WASH-OUT  CLOSET.  HOPPER  CLOSET. 

many  kinds  and  styles.  The  plunger  closet  is  a  modification 
of  the  old  pan  closet  in  which  the  bowl  is  omitted,  and  a  large 
body  of  water  is  released  when  the  plunger  is  raised.  In  the 
wash-out  and  hopper  closets  the  discharge  of  the  water  tank 
by  pulling  the  chain  gives  an  ample  amount  of  water  to  effect 
thorough  flushing.  The  hopper  closet  appears  to  take  the 
highest  rank  on  account  of  the  simplicity  of  its  construction, 
and  numerous  styles  of  it,  called  the  short  hopper,  the  long 
hopper,  the  wash-down,  and  the  syphon-jet  closet  are  found 
in  the  market.  The  water  is  admitted  in  all  cases  around  the 
rim,  but  some  styles  also  bring  in  a  jet  lower  down.  To 
avoid  syphonage  of  the  trap  an  opening  is  provided  to  which 
a  vent  pipe  is  attached,  this  pipe  running  to  the  vent  tube. 
A  closet  is  made  of  earthenware  with  a  porcelain  glaze  and 


146  SEWERAGE   SYSTEMS.  IV. 

so  built  that  no  portion  is  below  the  floor  line.  No  woodwork 
of  any  kind,  except  the  seat  and  lid,  is  needed  around  it  when 
placed  in  a  bath-room.  It  should  be  placed  near  the  main 
soil  pipe,  so  that  the  connection  between  them  is  short,  and  it 
is  important  that  the  waste  pipes  from  the  bath-tub  or  wash- 
stands  should  never  connect  to  the  discharge  pipe  of  the  closet, 
but  be  carried  independently  to  the  soil  pipe. 

In  hotels  and  public  buildings  the  closets  are  necessarily 
placed  in  stalls,  and  these  are  sometimes  of  wood,  although 
marble  or  slate  is  used  in  the  best  work.  No  stalls  for 
urinals,  however,  should  ever  be  made  of  wood.  In  spite  of 
all  these  precautions  a  certain  degree  of  attention  on  the  part 
of  a  servant  is  needed  to  secure  perfect  cleanliness. 

50.  HOUSE  DRAINAGE. 

House  drainage,  or  house  sewerage,  as  it  should  properly 
be  called,  embraces  all  those  pipes  and  connections  which 
carry  the  sewage  out  to  the  cesspool  or  the  sewer,  the  former 
being  the  destination  for  an  isolated  country  residence  and 
the  latter  for  a  city  house.  It  consists  of  two  parts,  an  iron 
pipe  within  the  house  which  extends  about  three  feet  beyond 
the  wall,  and  an  earthenware  pipe  which  extends  through  the 
ground  the  remainder  of  the  distance. 

The  soil  pipe  is  of  cast  iron,  4  inches  in  diameter,  with  lead 
joints.  It  projects  above  the  roof  of  the  house,  with  the  top 
open,  this  being  protected  by  a  basket  to  prevent  ingress  of 
birds  and  rats.  Through  the  house  it  is  vertical  until  the 
cellar  is  reached,  and  then  it  curves  so  as  to  pass  out  of  the 
wall  horizontally.  In  the  figure  are  shown  two  water  closets 
connecting  with  the  soil  pipe  at  A  and  C  and  a  kitchen  sink 
at  B\  at  D  is  a  trap  whose  lid  may  be  removed  if  an  obstruc- 
tion should  occur.  The  soil  pipe  should  be  everywhere  visi- 
ble except  at  the  places  where  it  passes  through  the  floors. 
It  should  not  be  carried  under  the  cellar  floor  except  when 


So. 


HOUSE   DRAINAGE. 


147 


connections  to  laundry  tubs  or  water  closets  demand  it;  in 
this  case  the  trap  D  should  be  made  easy  of  access  by  placing 
it  in  a  brick  box  with  a  cover  at  the  level  of  the  cellar  floor. 
These  precautions  render  it  impossible  for  any  leakage  to 


HOUSE-SEWERAGE  PIPES. 

occur  without  being  soon  detected,  and  make  the  plumbers' 
bill  for  repairs  much  smaller  than  if  a  wall  or  cellar  floor  has 
to  be  torn  to  pieces  and  rebuilt. 

A  fresh-air  inlet  pipe  FG  connects  the  soil  pipe  to  the 
external  air,  so  that  a  circulation  may  occur;  this  will  certainly 
take  place  if  the  soil  pipe  be  placed  near  the  house  chimney, 
whose  heat  will  render  the  air  in  it  higher  in  temperature  than 
that  outside  the  building.  By  this  method  oxygen  is  supplied 
to  attack  the  decaying  organic  matter  in  the  soil  pipe  and 
purify  it  by  combustion  and  nitrification.  Such  inlet  pipes 
may  be  placed  on  the  outside  edge  of  the  sidewalk  in  cities, 
and  no  offense  will  be  caused,  since  in  all  ordinary  cases  the 
air  of  the  street  is  entering  them  in  order  to  pass  out  again  at 
the  tops  of  the  houses. 

The  vent  tube,  shown  by  the  dotted  lines  at  HK,  is  also 
iron  and  usually  about  3  inches  in  diameter.  This  does  not 
act  in  any  respect  as  a  ventilating  flue,  but  its  office  is  merely 


148  SEWERAGE   SYSTEMS.  IV. 

to  bring  atmospheric  pressure  on  the  crowns  of  the  traps  and 
thus  prevent  their  syphonage.  This  vent  tube  may  be  joined 
to  the  soil  pipe  above  the  highest  fixture,  or  it  may  be  carried 
up  above  the  roof;  in  the  latter  case  it  is  well  to  make  it  4 
inches  in  diameter,  so  that  clogging  by  frost  or  snow  may  not 
occur. 

When  the  rainfall  on  the  roof  is  admitted  to  the  sewer  the 
water  leader  runs  down  on  the  outside  of  the  wall  and  dis- 
charges into  the  soil  pipe  near  E.  If  the  junction  is  made  by 
a  tight  connection  a  second  trap  may  be  inserted  beyond  it, 
but  it  is  often  preferred  that  the  rain  water  should  discharge 
into  a  small  manhole  which  is  connected  with  the  soil  pipe; 
either  of  these  arrangements  brings  the  atmospheric  pressure 
on  the  street  side  of  the  main  trap  D  and  thus  renders  it  less 
liable  to  syphonage. 

The  second  part  of  the  house-drainage  system  is  a  vitrified- 
clay  pipe,  called  the  drain  pipe,  which  extends  from  the  end 
of  the  iron  pipe  to  the  sewer;  this  is  4  inches  in  diameter,  or 
6  inches  for  hotels  and  very  large  houses;  it  is  laid  with 
cement  joints,  and  its  slope  should  not  be  less  than  3  feet  in 
100  feet.  When  this  pipe  goes  to  a  cesspool,  as  in  a  country 
house,  the  cesspool  should  have  a  vent  to  the  open  air. 

After  the  completion  of  a  house-sewerage  system,  but 
before  the  vent  and  drain  pipes  are  connected,  a  test  for  leak- 
age may  be  made.  This  is  done  by  stopping  the  end  of  the 
soil  pipe  and  all  fixture  outlets  and  vent  pipes,  and  then 
filling  the  soil  pipe  with  water  up  to  the  top  and  allowing  it 
to  remain  for  twenty-four  hours.  This  test  cannot  be  made 
in  freezing  weather,  and  it  is  often  an  awkward  operation  to 
undertake.  A  better  test  is  that  by  peppermint,  which  shows 
the  efficiency  of  both  traps  and  joints.  This  is  made  after  the 
work  is  entirely  completed  and  the  traps  filled,  and  consists 
simply  in  putting  about  half  an  ounce  of  oil  of  peppermint 
into  the  fresh-air  inlet  and  noting  whether  any  odor  is 


51.  CLASSIFICATION  OF  SYSTEMS.  149 

observed  in  the  house.  In  cases  where  there  is  no  fresh-air 
inlet  the  peppermint  may  be  put  into  the  lowest  house  fixture 
and  be  quickly  washed  down  with  water,  or  it  may  be  put  into 
the  cesspool  or  sewer.  The  man  who  handles  the  peppermint 
should  not  walk  through  the  house  until  after  the  close  of 
the  test. 

It  was  said  forty  years  ago  that  a  man's  happiness  was 
inversely  proportional  to  the  number  of  gas,  water,  and  sewer 
pipes  in  his  house.  This  saying  may  be  true  to-day  if  these 
modern  conveniences  be  put  into  the  house  with  the  main 
idea  of  cheapness,  without  a  definite  plan,  and  without  in- 
spection of  the  plumbers'  work.  In  many  cities  the  law 
requires  that  plans  and  specifications  for  house  drainage  must 
be  approved  by  the  board  of  health  or  by  the  inspectors  of 
buildings  before  work  can  be  begun,  that  the  plumber  em- 
ployed must  be  one  licensed  by  the  same  authority,  and  that 
official  inspections  must  be  made.  Under  this  plan  the 
house-sewerage  system  will  be  one  that  brings  comfort  and 
happiness  to  the  householder  and  promotes  the  health  of  the 
family  and  the  community.  The  same  result  can  be  secured 
when  plans  and  specifications  are  drawn  by  a  competent  archi- 
tect if  these  are  followed  by  a  strict  inspection  of  the  work 
of  the  plumber.  Here,  as  in  all  other  branches  of  sanitary 
engineering,  well-laid  plans  and  constant  inspection  in  execut- 
ing them  are  indispensable  in  order  to  secure  health  and 
happiness. 

51.  CLASSIFICATION  OF  SYSTEMS. 

In  Art.  48  it  was  shown  that  the  pail  method  for  the 
removal  of  excremental  matter  is  an  offensive  and  impracti- 
cable one,  and,  as  it  is  not  used  in  the  United  States,  it  will 
not  be  classed  among  the  public  systems.  The  cesspool  plan 
was  also  shown  to  be  an  objectionable  one  for  a  large  town  or 
city,  and,  although  it  is  still  extensively  used  in  villages  and 
country  districts,  it  is  to  be  regarded  as  a  family  method  rather 


I5O  SEWERAGE   SYSTEMS.  IV. 

than  a  practicable  and  efficient  public  system  and  hence  will 
receive  no  further  consideration.  There  remain,  then,  only 
the  systems  of  removal  by  means  of  the  public  water  supply, 
known  as  the  water-carriage  systems,  which  are  an  outgrowth 
of  the  plan  followed  in  ancient  Rome.  Had  these  ancient 
methods  been  continued  and  developed  throughout  Europe 
the  thousand  years  of  filth,  disease,  and  misery  known  as  the 
dark  ages  might  perhaps  have  been  a  thousand  years  of 
cleanliness,  health,  and  happiness. 

In  the  two  preceding  articles  the  arrangement  of  the  sewer- 
age fixtures  and  drains  of  a  modern  house  has  been  described, 
and  now  the  sewage  is  to  be  carried  by  the  street  sewers 
through  and  away  from  the  town.  This  sewage  is  mostly 
water  and  the  amount  of  it  is  practically  the  same  as  that  of 
the  water  supply  that  enters  the  house.  The  total  amount 
of  sewage  carried  away  from  the  houses  may  in  summer 
seasons  be  slightly  less  than  that  of  the  total  water  supply, 
owing  to  the  loss  by  evaporation  and  percolation  of  that  part 
used  for  sprinkling  lawns  and  streets,  but  it  is  a  fair  assump- 
tion to  take  the  two  amounts  as  equal. 

The  total  solids  in  an  analysis  of  sewage  may  be  stated  as 
about  1000  parts  per  million  for  an  average  figure,  and  rarely 
if  ever  do  they  exceed  5000  parts  per  million.  Hence  much 
more  than  99  per  cent  of  the  sewage  is  water,  and  all  the  laws 
of  hydraulics  are  directly  applicable  to  its  flow  through  the 
sewer  pipes.  The  oxygen  in  the  water  tends  to  decompose 
and  destroy  the  organic  matter,  but  the  supply  of  it  is  only 
sufficient  for  a  very  imperfect  purification,  and  hence  it  is 
important  to  remove  the  sewage  as  quickly  as  possible  out  of 
the  town  to  a  place  where  an  abundant  amount  of  oxygen  is 
available.  This  place,  in  all  the  ancient  sewerage  plants  and 
in  the  majority  of  the  modern  ones,  is  the  ocean  or  the  river, 
where  the  dilution  of  the  sewage  with  water  furnishes  suffi- 
cient oxygen  to  enable  the  useful  bacteria  to  complete  the 
work  of  turning  the  organic  matter  into  harmless  substances. 


51.  CLASSIFICATION   OF   SYSTEMS. 

The  water-carriage  systems  for  sewage  removal  may  be 
divided  into  two  classes,  gravity  systems  and  pumping 
systems.  A  gravity  system  is  one  where  the  flow  of  sewage 
takes  place  entirely  by  the  force  of  gravitation  in  the  same 
manner  as  that  of  water  in  a  conduit  or  pipe;  probably  more 
than  90  per  cent  of  all  sewerage  plants  are  gravity  systems 
and  they  are  always  used  when  there  is  sufficient  fall  from  the 
town  to  the  place  where  the  sewage  is  to  be  delivered.  A 
pumping  system  is  one  where  some  method  of  lifting  the 
sewage  is  required  either  on  account  of  the  low  location  of  the 
town  or  in  order  to  raise  it  so  that  it  may  be  purified  by  the 
methods  which  are  to  be  described  in  the  next  chapter.  In 
a  pumping  system  there  is  always  a  certain  amount  of  gravity 
action,  because  it  is  necessary  that  the  flow  from  the  houses 
must  be  collected  in  wells  before  it  can  be  pumped. 

Gravity  systems  are  divided  into  two  kinds,  called  the  com- 
bined system  and  the  separate  system.  In  the  combined 
system  the  sewers  carry  not  only  the  sewage,  but  also  the  rain 
water  which  falls  on  the  roofs  and  the  streets,  this  system  is 
hence  a  close  imitation  of  the  method  of  ancient  Rome.  In 
the  separate  system  the  sewers  carry  the  house  sewage,  while 
the  water  of  the  streets  is  entirely  excluded;  a  small  amount 
of  roof  water  may,  however,  be  admitted  in  order  to  assist  in 
flushing  the  pipes. 

A  pumping  system  carries  away  sewage,  which  is  collected 
in  wells  either  by  the  combined  or  separate  method,  by 
raising  it  to  the  required  height  to  insure  the  flow  out  of  the 
town.  Common  pumps  may  be  used  for  this  purpose,  but 
distinctive  pneumatic  methods  have  also  been  introduced. 
The  vacuum  system  is  a  suction  method  by  which  a  partial 
vacuum  is  formed  in  many  pipes  of  a  district  so  that  the 
atmospheric  pressure  may  lift  the  sewage.  The  compressed- 
air  system  is  a  method  by  which  air  pressure  is  transmitted 
through  a  series  of  pipes  to  vessels  where  the  sewage  has 
accumulated  and  thus  forces  it  up  to  a  higher  elevation. 


152  SEWERAGE   SYSTEMS.  IV. 

The  combined  and  separate  systems,  without  pumping,  are 
those  which  should  receive  the  main  attention  of  the  student 
on  account  of  their  more  extensive  use.  It  is  apparent  that 
the  combined  system  requires  larger  sewers  than  the  separate 
system,  and  also  that  when  the  latter  is  used  extra  provision 
must  be  made  for  disposing  of  the  storm  water  of  the  streets. 
In  some  cases  this  storm  water  may  be  left  to  take  care  of 
itself  by  natural  flow  in  the  streets,  but  in  others  a  special 
system  of  drains  may  be  necessary. 

The  main  use  of  a  sewerage  system  is,  of  course,  to  remove 
the  sewage  out  of  the  town  before  it  has  had  time  to  decom- 
pose, but  it  also  furnishes  an  important  incidental  advantage 
in  draining  the  soil.  The  evil  effects  of  wet  soil  and  damp 
cellars  are  well  known,  and  the  sewers  should  be  so  con- 
structed as  to  lower  the  level  of  the  ground  water  in  damp 
localities.  This  drainage  cannot  enter  the  sewers,  for  they 
should  be  made  water-tight  in  order  to  prevent  the  pollution 
of  the  soil,  but  the  sewer  foundation  can  be  so  arranged  as  to 
act  as  a  drain,  and  thus  to  greatly  decrease  the  dampness  of 
cellars  and  basements. 

52.  THE  COMBINED  SYSTEM. 

The  sewers  of  the  combined  system  are  to  carry  away  not 
only  the  sewage,  but  also  the  rain  that  falls  upon  the  roofs  and 
streets.  Hence  the  rain-water  leaders  are  directly  connected 
to  the  house  drain  pipe,  and  at  the  street  corners  basins  are 
constructed  to  receive  the  flow  of  the  gutters.  The  size  of 
the  sewers  in  this  system  depends  more  upon  the  storm  water 
than  upon  the  volume  of  the  house  sewage.  The  amount  of 
sewage  may  be  regarded  as  the  same  as  that  of  the  water 
supply,  say  100  gallons  per  person  per  day  as  the  mean 
amount,  and  180  or  200  gallons  per  person  per  day  as  the 
maximum  flow  on  Monday  forenoons.  The  amount  of  storm 
water  is  more  difficult  to  estimate,  but  a  common  method  is 


52.  THE   COMBINED   SYSTEM.  153 

to  take  one  inch  of  rainfall  per  hour  over  the  area  covered  by 
the  sewerage  system  and  to  consider  that  the  main  sewer  is 
to  carry  either  all  or  a  part  of  this  water.  As  noted  in  Art. 
16,  rainfalls  much  heavier  than  this  are  liable  to  occur,  but 
these  come  at  rare  intervals  and  are  of  short  duration,  so  that 
probably  one  inch  per  hour  is  a  fair  maximum  allowance  for 
sewer  capacity.  To  provide  for  an  excessive  rainfall  of  4  or 
5  inches  per  hour  will  involve  an  unwarranted  extra  expense, 
the  interest  on  which  would  be  more  than  enough  to  cover 
the  cost  of  street  repairs  rendered  necessary  by  heavy  storms 
of  rare  occurrence. 

In  the  design  of  a  combined  system  the  first  thing  is  to 
prepare  a  topographic  map  of  the  town  and  its  vicinity.  This 
map  shows  the  watershed  whose  storm  water  is  liable  to  reach 
the  sewer,  all  streets  and  houses,  and  the  contour  curves. 
For  a  flat  town  contours  at  vertical  intervals  of  one  foot  are 
needed  and  the  levels  by  which  these  are  determined  must  be 
run  with  "great  precision ;  for  a  hilly  or  sloping  town  contours 
at  intervals  of  two  or  three  feet  may  perhaps  be  sufficient. 
With  this  map  in  hand  the  engineer  is  able  to  make  profiles 
of  streets,  ascertain  the  available  slopes,  lay  out  the  lines  for 
the  main  and  lateral  sewers,  and  then  estimate  the  cost  of 
construction.  It  may  be  often  necessary  to  make  several 
plans  in  order  that  comparative  estimates  may  determine  the 
one  which  will  furnish  the  proper  efficiency  with  the  greatest 
degree  of  economy. 

The  directions  of  the  main  and  lateral  sewers  will  be  deter- 
mined by  the  topography  of  the  town.  The  simplest  case  is 
that  where  the  town  is  on  one  side  of  a  river  with  a  uniform 
slope  toward  it;  here  there  may  be  one  or  two  main  sewers 
running  directly  into  the  river,  and  this  is  called  a  perpen- 
dicular method  of  location.  The  more  usual  case  is  one  where 
the  main  sewer  runs  parallel  with  the  river  and  the  lateral 
sewers  run  into  it;  this  is  called  the  intercepting  method, 


154 


SEWERAGE   SYSTEMS. 


IV, 


because  the  main  sewer  takes  the  place  of  the  river  and  carries 

all  the  sewage  to  some  point  down 

the  stream.  In  order  to  relieve  the 
main  sewer  of  a  portion  of  the  storm 
water  the  arrangement  in  the  figure 
is  sometimes  used;  here  the  normal 
flow  of  sewage  is  caught,  but  when 
the  lateral  sewer  becomes  filled  after 
a  rain  a  portion  of  its  flow  is  discharged  over  the  top  of  the 
main  sewer  into  the  river. 

The  shapes  of  sewers  of  the  combined  system  are  circles  for 
the  small  sizes,  circular  or  egg-shaped  sections  for  the  medium 
sizes,  and  basket-handle  sections  for  the  large  sizes.  Circular 
sections  are  made  of  brick  when  over  three  feet  in  diameter, 


OVERFLOW  CONNECTION. 


SHAPES  OF  SEWERS. 

while  vitrified  clay  pipes  are  used  for  smaller  sizes.  Egg- 
shaped  sections  are  rarely  used  in  the  United  States ;  their  advan- 
tage consists  in  the  constant  hydraulic  radius  for  different 
depths  which  maintains  the  velocity  uniform  The  two  kinds 
of  basket-handle  sections  are  used  for  stiff  and  soft  soil,  as 
explained  in  Art,  37;  these  forms  offer  much  frictional  resist- 
ance to  the  flow  under  normal  conditions,  as  the  section  of 
sewage  alone  is  small  compared  to  the  area  of  the  entire  cross- 
section.  The  figure  shows  what  sometimes  occurs  in  one  of 
these  large  sewers  when  the  slope  is  slight,  a  large  deposit  of 
solid  matter  being  made  and  the  small  quantity  of  sewage 
flowing  in  a  channel  formed  upon  it.  During  a  period  of 


52.  THE   COMBINED    SYSTEM.  155 

prolonged  drought  these  deposits  may  accumulate,  unless 
hydrant  water  be  turned  in  to  remove  them,  so  as  to  pollute 
the  air  of  the  surrounding  neighborhood.  One  strong  objec- 
tion to  the  combined  system  is,  in  fact,  the  difficulty  of  keep- 
ing the  large  sewers  in  a  cleanly  condition  during  dry  seasons. 

Manholes  must  be  provided  at  all  points  of  junction,  and 
also  at  regular  intervals  along  the  lines,  in  order  that  access 
to  the  sewers  may  be  had.  A  manhole  also  serves  as  a  ven- 
tilator, it  being  covered  with  a  perforated  iron  plate,  through 
which  air  comes  out  and  enters.  Indeed  the  only  practicable 
method  of  ventilating  sewers  is  by  means  of  such  manholes; 
and  it  is  not  found  that  the  air  of  a  good  sewer  causes  any 
offense  in  the  streets.  The  constant  admission  of  fresh  air 
furnishes  oxygen  to  the  decomposing  matter  and  thus  secures 
deodorization  and  purification.  If  the  sewers  were  unventi- 
lated  and  fresh  air  not  admitted  an  interior  pressure  might 
result,  which  would  force  sewer  gas  back  into  the  soil  pipes 
of  the  houses  and  so  produce  evil  effects.  Sewer  gas  in  a 
house  is  most  injurious,  but  in  the  street,  where  a  constant 
supply  of  fresh  air  is  at  hand,  it  is  quickly  neutralized  and 
becomes  harmless. 

The  catch  basins  which  receive  the  storm  water  are  located 
at  the  street  corners  so  as  to  receive  the  flow  of  two  or  more 
gutters.  The  pipe  connecting  with  the  sewer  enters  at  one 
side  sufficiently  high  so  that  sand  and  gravel  may  collect  in 
the  bottom,  whence  it  is  removed  after  the  storm  has  ceased. 
Rubbish  may  be  kept  out  of  the  pipe  to  a  certain  extent  by 
curving  it  down  like  a  syphon  or  by  placing  a  basket  screen 
over  its  end. 

In  seacoast  towns,  where  the  main  sewer  discharges  below 
high  tide,  it  is  provided  with  a  flap  valve  at  the  end  to  pre- 
vent the  ingress  of  the  water,  and  thus  the  sewage  is  backed 
up  for  some  distance  until  the  tide  falls.  Sometimes  large 
tanks  are  built  to  receive  this  accumulation  and  store  it  for 


156  SEWERAGE  SYSTEMS.  IV. 

the  three  or  four  hours  during  which  the  outlet  is  covered  by 
the  tide. 

The  combined  system  is  best  adapted  to  large  cities  on  flat 
ground  where  the  storm  water  of  the  streets  may  cause  great 
damage  by  flooding  basements  and  sidewalk  vaults.  It  is  also 
well  adapted  to  towns  where  the  storm  water  cannot  be  other- 
wise diverted  so  as  to  prevent  similar  damages.  In  many 
towns  the  combined  system  has  been  a  slow  growth,  first 
starting  by  the  construction  of  a  sewer  to  carry  the  flow  of  a 
troublesome  brook.  As  has  been  remarked  before,  there  is 
nothing  in  any  system  which  renders  it  economical  or  advan- 
tageous in  all  cases,  but  in  each  case  the  engineer  is  to  make 
such  plans  as  will  best  fit  the  local  circumstances. 

53.  THE  SEPARATE  SYSTEM. 

The  separate  system  originated  in  England,  it  being  first 
proposed  by  Phillips  in  1849  and  recommended  by  him  as  a 
solution  of  the  difficulties  in  London,  where  large  drains  had 
been  built  to  carry  off  surface  water  only  and  hence  were  not 
well  adapted  to  receive  sewage.  Accordingly  he  maintained 
that  the  proper  solution  of  the  question  demanded  that  sew- 
age should  be  carried  in  a  new  system,  "  distinct  and  separate 
from  the  permeable  land  drains."  The  idea  was  not  carried 
out  in  London,  but  it  received  the  approval  of  some  engineers 
and  about  1870  such  sewerage  systems  were  constructed  at 
Oxford  and  a  few  other  English  cities.  In  America  the  first 
application  of  the  system  was  by  Waring  at  Memphis,  Tenn., 
in  1880.  As  in  the  case  of  all  new  improvements,  much  oppo- 
sition and  criticism  was  made,  but  the  cheapness  and  efficiency 
of  the  system  soon  overcame  these  objections,  so  that  since 
1885  hundreds  of  towns  have  been  sewered  on  this  plan. 

The  sewers  of  the  separate  system  are  to  carry  sewage 
only,  but  a  small  amount  of  additional  water  is  admitted  from 
flush  tanks  or  from  roofs  to  insure  cleanliness.  As  a  conse- 


53-  THE  SEPARATE   SYSTEM.  157 

quence  the  sewers  are  smaller  than  those  of  the  combined 
system,  being  rarely  larger  than  four  feet  in  diameter,  and  the 
cost  of  construction  is  materially  lowered.  Circular  sections 
are  used  almost  exclusively  and  for  all  the  common  sizes  these 
consist  of  clay  pipes  with  cement  joints. 

All  the  remarks  made  in  the  last  article  regarding  the  influ- 
ence of  topography  on  the  location  of  the  sewers  apply  equally 
well  to  the  separate  system.  The  rainfall  over  the  watershed 
area  is  not  to  be  considered,  however,  as  this  is  not  to  be 
admitted  to  the  sewers.  When  roof  water  is  taken  into  the 
sewers  for  the  purpose  of  flushing  this  is  done  only  at  a  few 
houses  near  the  dead  ends  of  the  lateral  lines,  and  only  the 
houses  designated  by  the  engineer  are  allowed  to  connect 
their  rain-water  leaders  with  the  drain  pipes. 

Manholes  are  provided,  as  in  the  combined  system,  at  all 
junctions  of  lateral  with  main  sewers  and  at  other  points  on 
the  line  from  300  to  500  feet  apart.  Through  these  manholes 
ventilation  takes  place,  and  they  also  give  access  to  the  sewers 
so  that  obstructions  may  be  removed.  A  special  form  of  air 


AIR  INLET.  LAMP-HOLE.  HAND-HOLE. 

inlet  is  likewise  often  used;  this  is  cheaper  than  a  manhole 
and  serves  the  same  purpose  as  far  as  ventilation  is  concerned ; 
this  consists  of  a  vertical  pipe  having  its  open  top  at  the  street 
surface  in  a  masonry  box  which  is  covered  with  a  perforated 
iron  lid. 

The  early  sewerage  plants  on  the  separate  system  suffered 
much  from  obstructions  caused  by  deposits  or  by  matter 
accumulating  at  a  defective  joint.  To  meet  this  difficulty 
manholes  were  constructed  at  closer  intervals,  so  that  rakes 


158  SEWERAGE   SYSTEMS.  IV. 

could  be  introduced  or  jets  from  a  hose  be  thrown  into  the 
pipes.  Lamp-holes  like  that  shown  in  the  above  figure  are 
also  built  between  the  manholes;  as  these  are  used  only  at 
rare  intervals,  the  cover  caps  are  placed  below  the  street  sur- 
face and  a  record  of  their  location  made.  Hand-holes  in  pipes 
may  be  likewise  inserted  between  the  lamp-holes  and  their 
location  be  recorded,  ,but  to  use  these  the  street  must  be 
torn  up. 

The  sewers  of  this  system  are  generally  designed  in  such 
sizes  that  they  will  be  about  half  full  when  the  maximum  flow 
occurs  on  Monday  forenoon.  Hence  the  capacity  is  amply 
sufficient  to  carry  double  the  mean  daily  water  consumption 
and  also  to  allow  for  the  future  growth  of  the  town.  The 
ordinary  flow  will  then  make  the  sewers  less  than  half  full, 
and  the  additional  water  needed  for  flushing  may  be  admitted 
either  during  the  maximum  or  minimum  flow.  It  has  been 
found  that  reliance  upon  roof  water  alone  is  not  satisfactory, 
and  that  regular  periodic  flushing  must  be  generally  made 
from  special  tanks.  In  fact  some  engineers  allow  no  roof 
water  at  all  to  enter  the  sewers,  and  probably  this  is  the 
wisest  plan. 

A  flush  tank;  is  placed  near  the  dead  end  of  a  lateral  sewer 
and  is  so  arranged  that  the  entire  contents  may  be  quickly 
discharged  into  it.  The  admission  of  the  water  to  the  tank 
is  so  regulated  that  it  may  take  several  hours,  a  day,  or  even 
longer  to  fill  it,  and  the  discharge  then  occurs  automatically. 
Several  of  these  flush  tanks  are  placed  throughout  the  town 
and  by  proper  regulation  of  the  entering  water  they  may  be 
made  to  act  separately  or  simultaneously,  as  experience  may 
determine  best.  They  are  built  of  masonry  in  the  street  and 
resemble  a  manhole  in  general  appearance.  The  water  is 
brought  by  a  small  pipe  from  the  street  main  and  its  faucet 
is  so  located  that  it  can  be  reached  by  taking  off  the  iron 
cover  of  the  tank. 


54- 


SIZES   OF  SEWERS. 


159 


There  are  numerous  styles  of  flush  tanks,  which  may  be 
classed  as  tilting,  syphon,  and  mechanical  tanks.     A  tilting 


TILTING  FLUSH  TANK.  SYPHON  FLUSH  TANK. 

tank  receives  the  water  in  an  iron  box  which  is  supported 
upon  a  knife-edge  pivot  at  each  end,  the  shape  of  the  box 
being  such  that  it  remains  horizontal  until  filled;  as  the  water 
is  admitted  the  center  of  gravity  of  the  box  and  water 
approaches  nearer  and  nearer  to  the  pivot  and  finally  when  it 
reaches  the  pivot  the  box  suddenly  tilts  and  discharges  its 
contents  into  the  sewer.  The  syphon  tank  shown  in  the 
figure  has  a  vertical  pipe  surrounded  by  a  bell,  the  annular 
space  between  these  constituting  the  syphon;  as  the  water  is 
admitted  it  gradually  rises  in  the  tank  until  the  top  of  the 
syphon  is  filled  and  then  runs  over  into  the  vertical  pipe  until 
the  lower  pool  is  filled ;  shortly  after  the  water  of  the  tank  is 
suddenly  discharged  into  the  sewer.  Mechanical  traps  depend 
upon  floats  or  valves  to  initiate  the  discharge,  and  they  are 
perhaps  more  liable  to  get  out  of  order  than  those  which 
depend  only  on  gravity  or  atmospheric  pressure.  The  tilting 
tanks  usually  discharge  from  100  to  200  gallons,  but  the 
syphon  tanks  are  of  larger  size  and  may  discharge  from  400 
to  500  gallons  in  less  than  one  minute. 


54.  SIZES  OF  SEWERS. 

The  flow  of  sewage  in  a  sewer  is  in  all  respects  controlled 
by  the  same  laws  which  govern  the  flow  of  water  in  aqueducts 
and  conduits.  The  sewer  must  be  on  a  uniform  slope,  for  the 
material  of  which  it  is  made  will  not  resist  the  interior  pres- 


i6o 


SEWERAGE   SYSTEMS. 


IV. 


sure  due  to  a  head,  and  moreover  such  head  could  not  exist 
without  flooding  the  cellars  along  the  line.  The  maximum 
flow  in  all  cases  occurs  when  the  sewer  is  nearly  but  not  quite 
full,  and  computations  made  by  regarding  it  as  full  are  hence 
on  the  safe  side. 

The  coefficients  of  discharge  for  clean  sewers  may  be  taken 
the  same  as  those  given  for  aqueducts  in  Art.  37.  The 
interior  surface  of  a  sewer,  however,  may  become  foul  in  time 
from  deposits  and  incrustations,  so  that  it  is  best  to  use  the 
smaller  values  given  in  the  following  table.  Here,  as  before, 

COEFFICIENTS  FOR  SEWERS. 


Hydraulic 
Radius  in 
feet. 

S  =  0.0001 

J  =  0.0020 

s  =  0.0004 

s  =  o.ooi 

S  =  0.01 

r  =  0.2 

68 

74 

78 

81 

81 

r  =  0.4 

86 

Qi 

94 

96 

98 

r  =  0.6 

95 

100 

102 

104 

1  06 

r  =  0.8 

103 

106 

1  10 

in 

112 

r  =  I 

109 

H3 

H5 

116 

117 

r  =  1.5 

120 

122 

123 

124 

125 

r  =  2 

127 

128 

129 

130 

130 

r  -  2.5 

132 

133 

134 

134 

134 

the  slope  s  is  the  ratio  of  the  fall  in  any  distance  to  that  dis- 
tance, and  the  hydraulic  radius  r  is  the  ratio  of  the  area  of 
the  cross-section  to  its  wetted  perimeter.  Thus  if  a  sewer 
has  a  fall  of  6  inches  in  100  feet  the  slope  is  s  =  0.5/100  = 
0.005;  if  tne  area  °f  its  cross-section  is  19.5  square  feet  and 
the  inner  perimeter  is  16.8  feet  the  hydraulic  radius  is  r  = 
19.5/16.8  =  1.16  feet;  then  from  the  table  the  coefficient  is 
c  =  119, 

By  the  use  of  the  above  table  and  the  formula  v  =  c  Vrs 
the  mean  velocity  v  is  computed  in  feet  per  second,  and  then 
the  discharge  q  follows  from  the  formula  q  =  av,  where  a  is 
the  area  of  the  cross-section.  In  a  case  of  design  q  is  given, 
and  here  the  values  of  a  and  r  are  to  be  found  by  trial  from 


J4-  SIZES  OF  SEWERS.  l6l 

the  equation  q  =  ca  Vrs.  For  circular  sections  a  solution  can 
also  be  made  by  inserting  for  a  and  r  their  values  in  terms  of 
the  diameter  d,  and  then  d  =  (%q/7rcs*)*. 

For  example,  take  a  town  of  8000  people  for  which  a  com- 
bined system  is  to  be  designed,  the  area  whose  storm  water 
is  to  be  carried  by  the  main  sewer  being  2  square  miles.  The 
maximum  flow  of  sewage  will  be  at  the  rate  of  I  600000 
gallons  per  day,  or  nearly  2.5  cubic  feet  per  second;  the  storm 
water,  at  the  rate  of  half  an  inch  of  rainfall  per  hour,  gives 
645  cubic  feet  per  second,  an  amount  so  large  that  the  sewage 
itself  is  unimportant  in  comparison.  By  the  use  of  the  above 
method  it  is  found  that  a  circular  sewer  about  7  feet  in 
diameter  on  a  slope  of  I  foot  in  100  feet  is  needed,  or  the 
diameter  should  be  about  n  feet  if  the  slope  be  I  foot  in 
1000  feet.  The  size  is  too  large  for  a  circular  section,  and 
hence  a  study  and  design  of  a  basket-handle  section  must 
be  made.  Indeed,  if  this  main  sewer  be  very  long  and  the 
slope  slight  its  cost  of  construction  might  become  too 
expensive  for  the  town,  and  accordingly  the  engineer  would 
be  obliged  to  reduce  the  amount  of  storm  water  which  it  is  to 
carry.  The  lateral  sewers  are  then  discussed  in  a  similar 
manner  and  each  made  of  such  size  as  to  dispose  of  the  flow 
of  its  district. 

In  the  separate  system  the  sewers  are  to  run  only  half  full 
under  maximum  flow;  hence  q=  ^avy  and  the  formula  for 
circular  sewers  becomes  d  =  (i6q/7tcs*)*.  For  the  above  data, 
where  q  =  2.5  cubic  feet  per  second,  this  gives  a  diameter  of 
about  14  inches  for  a  slope  of  o.oi  and  about  20  inches  for  a 
slope  of  o.ooi. 

The  slopes  and  shapes  of  sewers  ought  to  be  so  arranged 
that  the  mean  velocity  of  flow  shall  not  be  less  than  2  feet 
per  second,  for  if  the  velocity  be  smaller  sedimentation  occurs 
and  deposits  are  produced  which  in  time  may  become  obstruc- 
tions. Under  a  variable  flow  the  egg-shaped  section  is  a  good 


162  SEWERAGE   SYSTEMS.  IV. 

one  to  prevent  low  velocity,  because  the  hydraulic  radius  is 
larger  for  a  small  depth  of  sewage  than  a  circular  one.  The 
basket-handle  sections,  on  the  other  hand,  are  the  poorest 
forms  for  a  low  depth  of  flow,  as  then  the  velocity  becomes 
small  and  deposits  may  be  formed  in  the  manner  indicated  by 
the  last  figure  in  Art.  52. 

The  above  numerical  illustrations  show  clearly  the  great 
advantage  of  the  separate  system  in  cases  where  the  storm 
water  can  be  otherwise  readily  carried  away.  Small  size 
means  low  cost,  and  hence  it  is  that  the  separate  system  has 
been  so  widely  adopted  since  1885.  Indeed,  hundreds  of 
towns  which  would  now  be  using  the  old  cesspool  plan  if  the 
combined  system  of  sewerage  were  the  only  one  available 
have  adopted  and  built  an  efficient  system  for  the  removal  of 
house  sewage  on  the  separate  plan.  The  enormous  Cloaca 
maxima,  32  feet  in  height,  through  which  Nero  sailed  in  a 
stately  boat,  and  some  great  sewers  in  London  and  Paris 
which  may  be  also  navigated  by  smaller  boats,  no  longer  serve 
as  models,  but  they  teach  the  lesson  that  more  economical 
methods  might  undoubtedly  have  been  adopted. 

55.  CONSTRUCTION  OF  SEWERS. 

The  design  of  a  sewerage  system  involves  not  only  the 
determination  of  the  sizes,  but  detailed  working  drawings  of 
all  sections,  junctions,  manholes,  basins,  and  outlets.  When 
these  plans  have  been  prepared  and  the  specifications  drawn 
the  work  is  let  by  contract  to  the  lowest  responsible  bidder 
and  the  work  of  construction  begins.  It  is  not  the  intention 
here  to  discuss  the  hundreds  of  details  which  are  involved  in 
construction  work,  but  merely  td  note  a  few  points  which 
involve  general  principles  and  have  not  been  already  men- 
tioned. 

In  all  soft  and  yielding  soil  secure  foundations  must  be  pro- 
vided. A  pile  and  grillage  foundation  is  commonly  used  for 


55-  CONSTRUCTION   OF  SEWERS.  163 

both  small  and  large  sewers  in  wet  soil,  and  on  this  masonry 
or  concrete  may  be  laid  to  form  the  base  on  which  the  sewer 
rests.  In  slightly  yielding  soil  concrete  alone  may  be  suffi- 
cient, and  in  stiff  soil  the  sewer  may  be  laid  in  a  bed  of  earth 
carefully  excavated  to  the  shape  of  the  invert.  As  the  exact 
character  of  the  soil  may  not  be  known  until  the  excavations 
are  made,  general  plans  for  all  kinds  of  foundation  are  pre- 


SEWER  FOUNDATIONS. 

pared  in  advance,  and  then  each  is  built  at  the  place  desig- 
nated by  the  engineer. 

The  drainage  of  the  subsoil  is  to  be  provided  for,  when 
necessary,  by  stone  or  tile  drains  under  the  sewer,  as  indicated 
in  the  right-hand  diagram  of  the  above  figure.  The  sewers 
themselves  must  be  impermeable  to  water,  for  if  water  can 
enter  sewage  will  leak  out  and  thus  cause  pollution  of  the  soil 
of  the  street. 

In  the  combined  system,  brick  or  concrete  sewers  are  gener- 
ally used  for  all  sizes  greater  than  about  three  feet  in  diameter. 
For  brick  sewers  the  thickness  is  usually  8  inches  for  the  small 
sewers  and  12  inches  for  the  largest  ones.  For  concrete 
sewers  there  can  be  no  standard  rule  as  the  shape  of  the 
sewer,  the  amount  and  position  of  the  reinforcement,  if  this 
is  used,  the  pressure  of  the  soil  and  other  factors,  influence 
the  design  to  such  an  extent  as  to  make  each  sewer  a  separate 
problem.  Brick  and  concrete  sewers  are  necessarily  built  on 
forms  or  centers  which  are  removed  and  rebuilt  as  the  work 
advances. 


164  SEWERAGE    SYSTEMS.  IV. 

Concrete  pipe  from  two  to  seven  feet  in  diameter  has  been 
used  to  a  considerable  extent,  the  pipe  being  built  outside  of 
the  trench  and  laid  in  much  the  same  way  as  vitrified  clay 
pipe.  These  are  usually  reinforced  with  steel  rods,  expanded 
metal  or  woven  wire.  There  are  several  styles  of  concrete 
pipe  which  have  been  patented,  and  of  these  the  "  lock-joint " 
pipe  is  probably  the  most  generally  used.  When  concrete  is 
used  for  sewers,  great  care  is  necessary  to  make  the  sewer 
water-tight,  and  to  this  end  the  concrete  should  be  of  a  dense 
mixture.  The  invert  should  consist  of  a  rich  mortar  which 
should  be  trowelled  smooth. 

The  small  lateral  sewers  of  the  combined  syjtem,  and  all 
but  the  very  largest  sizes  of  the  separate  system,  are  made  by 
joining  together  vitrified  clay  pipes.  These  are  usually  3  feet 
long  and  have  bell  and  spigot  ends  which  are  connected  by 
cement  joints;  in  ordinary  soil  they  need  no  foundation  other 
than  the  bed  of  the  trench.  When  passing  under  a  railroad 
embankment,  or  in  any  place  where  shocks  are  liable  to  break 
the  pipe,  cast-iron  water  pipes  should  be  used  instead  of  clay 
ones. 

The  depth  of  a  sewer  below  the  street  surface  must  be  such 
that  its  crown  is  at  least  one  or  two  feet  below  the  level  of 
the  cellar  floors  in  order  that  these  may  be  effectively  drained, 
and  this  generally  demands  a  minimum  depth  of  8  or  9  feet. 
As  the  slope  of  the  sewer  is  to  be  uniform  throughout  its 
length,  it  may  be  difficult  to  secure  this  depth  in  a  street  with 
irregular  profile.  A  sewer  is  ordinarily  built  in  a  trench,  but 
occasionally  it  is  laid  near  the  surface  and  covered  with  an 
embankment,  and  sometimes  tunnel  work  is  necessary. 

All  manholes,  catch  basins,  and  flush  tanks  are  built  on 
good  foundations  with  stone  or  brick  masonry.  For  the  large 
sewers  a  manhole  is  an  upward  extension  of  the  sewer  itself, 
but  for  the  small  ones  it  is  built  independently  and  the  clay 
pipes  carried  into  and  out  of  it  at  slightly  different  levels. 


56.  VENTILATION  AND  CLEANING.  165 

Branch  hubs  for  the  house  drains  are  put  on  the  sides  of  the 
sewers  and  above  the  middle  at  intervals  of  25  feet  along  the 
line  or  opposite  every  lot  where  a  connection  may  be  hereafter 
made,  and  these  are  covered  by  a  cap  before  the  trench  is 
filled. 

The  lines  and  grades  for  the  work  are  given  by  the  engineer 
and  his  assistants,  who  also  exercise  a  constant  inspection  on 
the  materials  and  workmanship  and  see  that  the  plans  and 
specifications  are  fully  carried  out.  Books  on  construction 
give  many  details  regarding  brick,  stone,  cement,  and  their 
uses,  but  the  greater  part  of  the  knowledge  of  the  inspector 
is  not  and  cannot  be  learned  from  books;  it  must  be  gathered 
in  the  stern  school  of  experience.  The  construction  and  in- 
spection of  a  sewerage  system  are  not  unimportant  because  it 
is  buried  in  the  ground  as  soon  as  it  is  built;  but  rather  the 
most  painstaking  care  and  vigilant  inspection  should  be  exer- 
cised in  order  that  no  hidden  defects  may  mar  its  successful 
operation. 

56.  VENTILATION  AND  CLEANING. 

In  the  early  days  of  sewerage  systems,  that  is  to  say  before 
1870,  much  trouble  occurred  from  the  sewer  gas  forcing  its 
way  into  the  houses  and  creating  offense  in  the  streets. 
This  was  due  to  a  number  of  causes:  first,  the  house  plumb- 
ing was  imperfect  and  inefficient ;  second,  the  sewers  were  so 
large  as  to  become  very  foul  in  dry  seasons;  and  third,  the 
manholes  and  air  inlets  were  so  few  in  number  that  sufficient 
air  was  not  supplied  to  effect  deodorization.  When  sewer 
gas  did  escape  in  a  narrow  street  of  a  European  city  its 
volume  was  large  and  the  offense  was  noticed  at  the  windows 
of  the  houses. 

In  order  to  overcome  these  troubles  many  methods  for  the 
ventilation  of  sewers  were  tried  in  Europe.  Tall  chimneys 
were  built  near  the  ends  of  a  sewer,  and  pipes  were  carried 


1 66  SEWERAGE   SYSTEMS.  IV. 

up  on  house  walls  along  the  line,  to  create  a  draft.  Suction 
fans  driven  by  windmills- or  steam  engines  were  used  to  draw 
the  air  out  of  the  sewers.  The  chimney  plan  did  not  usually 
produce  the  required  draft,  and  the  suction  plan  produced  at 
some  places  a  draft  so  great  as.to  syphon  all  the  house-traps 
and  at  other  places  an  insufficient  circulation.  In  time  all 
these  methods  were  practically  abandoned,  although  a  few 
chimneys  may  yet  be  found  in  Europe,  and  the  fan  method 
was  very  recently  still  in  operation  for  a  few  of  the  sewers  of 
London. 

Various  chemical  expedients  were  also  attempted  to  de- 
odorize and  neutralize  the  sewer  gases  before  they  escaped 
into  the  streets.  Trays  filled  with  charcoal  powder  were 
placed  under  the  manhole  covers.  Chlorine  and  sulphur 
gases,  iron  carbides,  and  other  substances  were  advocated  and 
tried.  All  these  methods  likewise  proved  expensive  and 
inefficient,  and  their  use  has  hence  been  very  limited. 

The  idea  which  mainly  governed  these  early  methods  was 
the  mistaken  one  that  the  sewer  gas  should  not  be  allowed  to 
escape  into  the  streets.  As  soon  as  the  falsity  of  this  idea 
was  recognized,  and  perforated  manhole  covers  and  fresh-air 
inlets  were  provided,  the  problem  of  sewer  ventilation  was 
solved.  As  soon  as  the  house-drainage  system  was  provided 
with  proper  traps,  vent  tubes,  and  inlet  pipes  the  house  was 
protected  against  the  sewer  gas.  Some  of  the  gas  escapes 
into  the  streets,  it  is  true,  but  the  gas  from  fresh  sewage  is 
not  more  dangerous  than  that  of  the  odor  and  dust  from  the 
animal  excrements  which  are  constantly  dropped  upon  the 
pavements.  If  there  be  many  of  these,  openings  the  gas 
escaping  from  each  is  small  in  volume  and  the  oxygen  of  the 
air  deodorizes  it  far  more  efficiently  than  a  large  volume  can 
be  neutralized  by  artificial  chemical  treatment. 

The  gas  from  sewage  in  an  advanced  stage  of  decomposition 
is  offensive  and  dangerous,  and  the  method  for  keeping  this 


56.  VENTILATION   AND   CLEANING.  l6/ 

out  of  the  streets  is  to  prevent  its  formation.  If  the  sewage 
flows  so  rapidly  that  deposits  cannot  occur  it  will  be  removed 
from  the  town  before  the  dangerous  state  of  decomposition  is 
reached,  and  to  secure  the  necessary  velocity  of  flow  is  one  of 
the  important  problems  in  the  design  of  the  shape  and  size  of 
the  sewers.  In  the  large  sewers  of  the  combined  system  this 
is  often  difficult,  and  even  in  the  small  sewers  of  the  separate 
system  some  deposits  are  apt  to  form  which  may  be  the  cause 
of  obstructing  the  flow.  Hence  cleaning  or  flushing  the 
sewers  may  be  necessary  from  time  to  time. 

In  the  combined  system  the  main  reliance  upon  flushing  is 
the  storm  water,  and  when  this  conies  the  velocity  is  so 
increased  that  thorough  cleaning  is  done.  During  a  dry 
season,  however,  artificial  flushing  is  often  resorted  to.  This 
is  done  by  building  a  dam  in  a  manhole  and  arranging  in  it  a 
sluice  gate  so  that  it  may  be  raised  from  the  surface.  The 
sewage  then  backs  up  and  hydrant  streams  are  turned  in  at 
manholes  above  the  dam ;  then  when  the  gate  is  raised  the 
rush  of  water  scours  out  the  sewer.  Sometimes  permanent 
dams  with  sluice  gates  are  built  in  large  special  manholes, 
called  penstocks,  so  that  they  can  be  put  into  operation  with 
less  expense  than  a  temporary  construction.  If  the  sewer 
be  a  small  one  hydrant  streams  alone  may  often  do  much 
good  work,  particularly  if  the  deposits  can  be  stirred  by  rakes 
while  the  increased  volume  is  flowing. 

In  the  separate  system  the  flush  tanks  described  in  Art.  53 
are  in  daily  operation  and  hence  the  sewers  are  always  cleaner 
than  those  of  the  combined  system.  Such  flush  tanks  can 
also  be  put  at  the  dead  ends  of  the  lateral  sewers  of  the  com- 
bined system,  but  this  is  an  uncommon  practice.  When  an 
obstruction  occurs  in  the  sewers  of  the  separate  system  man- 
holes and  lamp-holes  enable  the  location  to  be  closely  deter- 
mined, and  if  rakes  and  water  jets  fail  to  remove  it  the 
hand-holes  are  used  as  a  last  resort. 


168  SEWERAGE   SYSTEMS.  IV. 

It  is  seen  from  these  brief  discussions  that  the  operation  of 
a  sewerage  plant  is  a  matter  which  requires  the  careful  intelli- 
gent supervision  of  the  city  engineer.  The  designing  engineer 
does  his  best  to  render  the  sewers  self-cleaning  by  making  the 
slopes  and  sizes  such  as  not  to  allow  a  low  velocity  of  flow; 
the  constructing  engineer  does  his  best  to  carry  out  these 
plans  and  to  secure  such  workmanship  as  will  prevent  all 
obstructions;  but  yet  maintenance  cannot  be  neglected. 
The  combined  system  has  catch  basins  which  must  be  cleaned 
and  large  sewers  whose  condition  with  regard  to  deposits 
should  always  be  known.  The  separate  system  has  flush 
tanks  whose  discharge  must  be  regulated  from  time  to  time 
and  manholes  which  must  constantly  be  kept  under  inspection. 
In  times  of  unusual  rainfall  the  combined  system  may  fail  to 
carry  the  storm  water  and  cause  cellars  to  be  flooded,  and  on 
occasions  of  serious  obstructions  the  sewers  of  the  separate 
system  may  back  the  sewage  into  basements  through  the 
drain  pipes.  To  guard  against  all  these  contingencies  and 
reduce  their  effects  to  a  minimum  the  town  or  city  engineer 
must  exercise  constant  and  vigilant  care. 

57.  PUMPING  OF  SEWAGE. 

When  a  town  is  very  flat  it  may  be  impossible  to  carry  away 
the  sewage  by  gravity  and  hence  some  method  of  pumping  is 
required.  In  this  article  methods  for  doing  this  by -common 
pumps  are  to  be  briefly  discussed.  The  sewage  is  collected 
either  by  the  combined  or  separate  system  and  carried  by 
gravity  to  wells,  and  from  these  wells  it  is  lifted  through  a 
pipe  to  the  place  and  height  required.  In  some  cases  it  may 
be  possible  to  carry  away  part  of  the  sewage  of  a  town  by 
gravity,  while  another  part  from  a  low  district  may  have  to 
be  lifted  a  few  feet  in  order  to  enable  it  to  get  into  the  main 
sewer.  At  London,  England,  a  large  part  of  the  ordinary 
sewage  flow  has  been  pumped  for  many  years;  and  in  many 


57.  PUMPING  OF  SEWAGE.  169 

European  and  American  cities  on  the  seacoast  or  along  large 
rivers  more  or  less  lifting  of  sewage  is  done.  At  Boston, 
Mass.,  one  half  of  the  sewage  is  lifted  35  feet  so  as  to  dis- 
charge it  into  the  ocean  at  high  tide. 

The  sewer  pipe  which  enters  the  wells  is  provided  with  a 
box  at  its  ends,  this  box  having  screens  to  collect  the  coarse 
matter  in  the  sewage.  This  matter  consists  largely  of  rags 
which  are  thrown  into  the  house  drains  by  careless  people, 
together  with  sticks,  lemon  peel,  and  similar  articles. 

Another  method  of  screening  or  straining  is  to  pass  the 
sewage  through  beds  of  coke;  this  is  used  when  the  sewage  is 
to  be  lifted  to  filter  beds  where  it  is  to  be  purified.  la  this 
case  the  iron  screens  intercept  the  rags  and  coarser  matter, 
while  the  finer  suspended  matter  and  some  of  the  dissolved 
impurities  are  absorbed  by  the  coke.  The  coke  must  be 
removed  from  time  to  time  whenever  it  becomes  clogged. 

As  the  sewage  is  mainly  water,  all  the  laws  of  hydraulics  are 
applicable  to  its  flow  in  pipes,  and  hence  the  computations 
are  the  same  as  for  pumping  water  from  a  river  to  a  reservoir. 
The  force  pumps  also  do  not  differ  in  principle  from  those 
used  for, water,  but  their  cylinders  are  generally  provided  with 
hand-holes,  which  may  be  easily  opened  to  clean  the  interior. 

When  the  height  of  lift  is  low  the  centrifugal  pump  is  an 
economical  and  efficient  one.  This  is  similar  in  principle  to 
a  turbine  water  wheel,  except  that  in  the  turbine  power  is 
produced  by  falling  water,  while  in  the  centrifugal  pump  the 
power  is  expended  in  order  to  raise  water.  A  series  of  vanes 
arranged  on  a  wheel  and  inclosed  in  a  case  is  set  in  motion 
by  the  power,  and  this  lifts  the  water  through  the  suction  pipe 
A,  whence  it  enters  the  end  of  the  case  at  B  and  is  then  forced 
up  the  discharge  pipe  C.  At  Chicago,  111.,  centrifugal  pumps 
have  been  used  to  lift  the  sewage  into  the  old  drainage  canal 
that  runs  southward  away  from  the  city. 

Syphons  may  be  sometim'es  used  to  carry  sewage  over  a 


SEWERAGE   SYSTEMS. 


IV. 


low  lift  by  atmospheric  pressure,  but  it  is  necessary  for  their 
successful  action  that  a  .pump  should  be  at  hand  in  order  to 
start  the  flow  when  it  becomes  interrupted.  The  Archimedean 


CENTRIFUGAL  PUMP. 

screw  is  another  device  that  may  be  used  by  a  low  lift,  but 
the  operation  of  this  by  steam  power  is  not  economical. 

The  expense  of  the  installation  and  operation  of  a  pump 
for  lifting  sewage  is,  of  course,  a  material  addition  to  that  of 
its  removal  by  gravity,  but  it  is  never  as  great  as  that  of 
pumping  the  water  supply,  since  the  lift  is  much  lower.  As 
a  rough  rule  about  10  cents  is  the  cost  of  lifting  I  ooo  ooo 
gallons  of  water  or  sewage  to  a  height  of  one  foot,  and  on 
this  basis  the  annual  cost  of  lifting  to  a  height  of  15  feet  the 
sewage  of  a  town  of  20  ooo  people,  not  including  storm  water, 
would  be  about  $i  i  ooo. 


58.  VACUUM  SYSTEMS. 

The  vacuum  method  of  pumping  is  of  course  applied  in 
every  suction  pump,  but  its  extension  on  a  large  scale  to  the 
collection  and  removal  of  the  sewage  of  a  town  involves  some 
new  ideas.  These  systems  originated  in  Holland,  where 
many  towns  are  below  the  level  of  the  ocean,  and  hence  require 
constant  pumping  of  some  kind  to  remove  their  sewage. 
Originating  there  about  1870,  the  systems  have  spread  to 
Belgium  and  France,  and  have  been  so  developed  that  they 
are  claimed  to  be  efficient  and  economical  under  the  conditions 
which  there  prevail. 


58. 


VACUUM   SYSTEMS. 


171 


The  oldest  vacuum  system  is  that  of  Liernur.  It  employs 
a  series  of  cast-iron  pipes  about  5  inches  in  .diameter,  from 
which  the  air  is  exhausted  by  air  pumps  at  a  central  station. 
These  vacuum  pipes  lead  from  closed  basins  at  the  street 
intersections  to  a  large  collecting  well,  out  of  which  the 
sewage  may  run  by  gravity  into  the  ocean  or  upon  the  filter 
beds  where  it  is  to  be  purified.  The  figure  represents  one  of 
the  closed  basins,  or  evacuators,  as  they  are  called;  this  is 
made  of  cast  iron  and  is  about  3  feet  in  diameter  and  3  feet 
high.  From  the  houses  the  sewage  flows  by  gravity  through 


LIERNUR'S  EVACUATOR. 

the  street  pipes  AA  into  the  evacuator,  from  which  it  is  to 
pass  out  through  the  vacuum  pipe  B.  When  the  evacuator 
is  filling,  the  valves  in  A  A  are  open,  while  that  in  ^'is  closed; 
when  it  is  to  be  discharged  the  valves  in  AA  are  closed  and 
those  in  B  and  C  are  opened,  and  then  the  atmospheric  pres- 
sure drives  out  the  sewage  through  the  vacuum  pipe  to  the 
collecting  well.  The  evacuators  are  discharged  one  at  a  time 
by  the  men  in  their  daily  rounds,  and  during  this  period  the 
air  pumps  keep  a  constant  vacuum  in  all  of  the  vacuum  pipes. 
Liernur's  system  was  not  designed  to  remove  the  liquid 
kitchen  wastes,  but  merely  faecal  matter  with  only  a  slight 
dilution  of  water.  As  the  evacuator  was  not  large  enough  to 
receive  the  accumulation  from  many  houses,  the  street  pipes 


tJ2  SEWERAGE  SYSTEMS.  IV. 

held  the  surplus,  and  then  by  proper  manipulation  of  the 
valves  these  ware  emptied  one  by  one  into  the  evacuator. 
This  plan  brought  a  suction  on  the  house  traps,  and  special 
valves  were  required  to  prevent  their  syphonage.  In  Am- 
sterdam six  of  these  plants  were  installed,  each  serving  about 
5000  people,  and  the  sale  of  the  excrement  as  a  fertilizer 
served  to  materially  reduce  the  expense  of  operation. 

The  vacuum  system  of  Berlier  is  based  on  the  same  idea  as 
that  of  Liernur,  but  the  details  are  very  different.      The  par- 
tial  vacuum    was    continuously  maintained 
in   the   street   pipes,    and   the   basins   were 
made  smaller  and  one  placed  in  the  cellar  of 
*     each  house.     At  the  bottom  of  the  basin,  or 


evacuator,  is  a  rubber  ball  attached  to  a 
float  which  is  raised  when  the  evacuator  is 
sufficiently  filled,  and  then  the  atmospheric 

BERLIER'S  pressure    forces    the   contents   through    the 

EVACUATOR. 

vacuum    pipes    to    the  collecting  well.      It 

was  the  intention  to  make  the  system  entirely  automatic,  but 
as  actually  built  the  material  passes  through  a  straining  box 
before  reaching  the  evacuator,  and  the  cleaning  of  this  box 
has  caused  considerable  nuisance.  Nevertheless  this  system 
has  been  used  in  certain  districts  of  Lyons  and  Paris  with 
some  degree  of  success. 

Vacuum  systems  have  not  been  used  in  America,  and 
since  1885  their  extension  has  been  very  slight  in  Europe. 
Perhaps  this  is  due  in  some  measure  to  the  circumstance  that 
their  use  has  been  limited  to  excreta  only,  leaving  the  kitchen 
wastes  to  be  disposed  of  by  some  other  method.  The  Berlier 
system  does  not  appear  to  be  a  more  reliable  method  than 
that  of  Liernur,  for  an  evacuator  in  the  cellar  must  even  under 
the  best  conditions  be  productive  of  some  trouble.  Neither 
system  can  compete  in  cleanliness  and  efficiency  with  that  of 
pumping  by  the  compressed-air  method. 


59- 


THE  COMPRESSED-AIR  SYSTEM. 


173 


59.  THE  COMPRESSED-AIR  SYSTEM. 

The  system  of  carrying  away  sewage  by  the  action  of  com- 
pressed air  was  invented  by  Shone  in  1878,  and  is  generally 
called  the  Shone  system.  It  has  been  used  in  a  number  of 
cities  in  England  and  in  two  or  three  in  America,  notably  at 
the  World's  Fair  held  in  Chicago  in  1893.  It  consists  of  the 
combination  of  the  separate  gravity  system  with  a  method  of 
pumping  by  compressed  air,  and  has  proved  to  be  more 
efficient  and  reliable  than  the  vacuum  systems  above 
described. 

A  separate  system  of  sewers  is  built  in  the  usual  way  over 
a  small  district  and  carries  the  sewage  to  a  closed  basin,  called 
an  ejector,  in  which  it  continues  to  accumulate  until  a  valve 
is  opened  by  a  float.  The  opening  of  this  valve  allows  com- 
pressed air  to  enter,  and  this  drives  out  the  sewage  through  a 
discharge  pipe  to  the  place  where  it  is  desired  to  deliver  it. 
In  the  following  figure  the  level 
of  the  sewage  which  is  shown  is 
the  lowest  limit  immediately  after 
a  discharge.  The  sewage  enters 
through  the  inlet  pipe  AB  until  A 
the  float  C  is  lifted  on  the  spindle 
against  the  bell  D,  and  this  opens 
the  valve  E,  through  which  the 
compressed  air  enters.  The  pres- 
sure of  this  air  closes  the  valve  B 
and  opens  F,  and  then  the  sewage  is  driven  through  the  dis- 
charge pipe  FG.  As  soon  as  the  float  falls  to  the  level  C  its 
weight  acts  on  the  spindle  so  as  to  close  the  valve  E\  then 
the  valve  F  falls  by  it  own  weight  to  prevent  the  sewage  from 
returning  to  the  ejector,  and  B  is  opened  by  the  inflowing 
sewage. 

The  largest  installation  of  the  Shone  system  was  that  at  the 


B 


SHONE' s  EJECTOR. 


1/4  SEWERAGE  SYSTEMS.  IV. 

World's  Fair  in  Chicago  in  1893.  The  site  was  flat,  and  it 
was  not  desirable  to  turn  the  sewage  into  Lake  Michigan 
without  purification,  and  hence  it  was  necessary  to  lift  it  to 
precipitation  tanks,  which  was  very  effectively  done  by  this 
method  of  pumping  with  compressed  air.  The  separate 
sewage  system  leading  from  the  buildings  to  the  ejector 
stations  was  laid  with  clay  pipes  6  and  8  inches  in  diameter, 
there  being  altogether  3  miles  of  such  sewer  pipe.  The 
ejector  stations  were  26  in  number,  each  having  two  ejectors, 
and  there  were' 5  miles  of  cast-iron  pipes  from  3  to  10  inches 
in  diameter  connecting  them  with  the  central  station  where 
the  air  was  compressed.  From  the  ejectors  to  the  precipita- 
tion tanks  there  were  4.8  miles  of  cast-iron  discharge  pipes 
varying  in  diameter  from  6  to  30  inches.  The  lift  from  the 
lowest  ejector  to  the  top  of  the  tanks  was  67^  feet,  and  the 
total  head  both  static  and  frictional  about  108  feet.  The 
capacity  of  the  plant  was  sufficient  to  dispose  of  the  sewage 
of  600  ooo  people  at  the  rate  of  14  gallons  per  person  per  day. 
There  can  be  no  doubt  that  the  Shone  system  is  a  most 
efficient  one  for  carrying  sewage  away  from  a  flat  site  or  lift- 
ing it  to  precipitation  tanks.  The  action  of  the  compressed 
air  is  entirely  confined  to  the  ejector  and  discharge  pipes  and 
it  can  produce  no  effect  on  the  house  traps.  The  method  is 
hence  really  one  for  pumping  alone,  and  its  success  depends 
upon  its  combination  with  the  gravity  separate  system  by 
means  of  the  automatic  ejectors.  While  the  method  is 
efficient,  it  is  very  costly  in  both  construction  and  operation. 
Duplicate  ejectors  are  necessary,  so  that  if  one  be  out  of  order 
the  other  may  continue  to  pump,  and  the  expenses  of  the  air- 
compression  plant  are  large.  However,  when  sewage  is  to  be 
pumped  to  any  considerable  height,  and  when  the  sewerage 
system  of  the  district  can  be  advantageously  arranged  for 
ejector  stations,  it  is  probable  that  the  Shone  method  can 
economically  compete  with  other  methods  of  pumping. 


6o.  COST  AND  ASSESSMENTS. 


60.  COST  AND  ASSESSMENTS. 

The  cost  of  sewerage  systems  of  different  towns  may  be 
compared  on  the  basis  of  the  length  of  the  sewers  or  on  that 
of  the  population.  By  the  first  method  the  total  cost  of  the 
system  is  divided  by  the  number  of  linear  feet  of  sewers,  and 
by  the  second  method  it  is  divided  by  the  population  of  the 
town.  A  combined  system  usually  costs  from  $3  to  $6  per 
linear  foot  of  sewer.  A  separate  system  usually  costs  from 
$0.50  to  $i  per  linear  foot  of  sewer,  but  to  this  must  be  added 
the  cost  of  drains  which  are  needed  to  dispose  of  the  storm 
water.  The  cost  of  pumping  and  of  purification  works,  if 
these  are  required,  is  to  be  added  to  the  above  figures. 

It  is  not  possible  to  say  in  advance  that  the  separate  system 
will  prove  more  advantageous  and  economical  for  a  given 
town.  To  decide  this  question  a  study  of  the  topography 
and  local  conditions  must  be  made  by  the  engineer,  with  due 
regard  to  the  experience  of  the  town  in  regard  to  its  storm 
water,  and  then  comparative  designs  and  estimates  of  cost 
will  enable  a  decision  to  be  made.  There  can  be  no  doubt 
that  the  tendency  has  been  decidedly  toward  the  separate 
and  away  from  the  combined  system  since  1890,  and  it  is 
hence  advisable  to  give  careful  attention  to  estimates  for 
carrying  away  the  sewage  and  storm  water  by  distinct  and 
separate  methods. 

The  expense  of  a  sewerage  system  is  to  be  met  on  a  differ- 
ent plan  from  that  of  a  water-supply  system.  Everyone 
expects  to  pay  an  annual  fee  for  the  use  of  water,  but  few  are 
willing  to  do  so  in  order  to  carry  away  sewage.  A  town  can 
usually  obtain  authority  to  issue  bonds  for  a  water  supply, 
because  an  annual  income  is  assured  which  will  pay  the 
interest  and  probably  yield  a  profit.  The  sewerage  system, 
however,  yields  no  income  in  American  cities,  although  in 
Europe  some  cities  collect  an  annual  fee  from  each  house 


1^6  SEWERAGE   SYSTEMS.  IV. 

connection,  but  it  is  the  source  of  an  annual  loss  in  expenses 
of  operation.  For  these  reasons  the  progress  of  sewerage  is 
slower  than  that  of  water  supply,  and  much  agitation  among 
taxpayers  is  required  to  induce  them  to  authorize  the  muni- 
cipality to  assume  the  financial  burden. 

The  expense  of  the  construction  of  the  sewerage  system  is 
too  great  to  be  met  by  taxes  in  a  single  year,  but  these 
should  be  spread  over  several  years,  and  hence  bonds  are 
issued  to  meet  the  outlay.  The  extra  tax  should  be  sufficient 
to  meet  the  annual  interest  on  the  bonds,  and  also  to  estab- 
lish a  sinking  fund  which  will  redeem  them  at  maturity.  For 
example,  consider  the  case  of  a  town  of  20  ooo  people  whose 
property  has  the  assessed  valuation  of  $3  500  ooo  and  whose 
average  annual  tax  is  15  mills  on  the  dollar,  and  suppose  that 
a  system  of  sewerage  is  to  cost  $60  OOO.  If  bonds  are  issued 
at  5  per  cent  per  annum  and  payable  in  2O  years  the  addi- 
tional annual  tax  must  be  sufficient  to  pay  the  annual  interest 
of  $3000  and  also  make  an  annual  contribution  to  a  sinking 
fund  which  at  the  end  of  20  years  will  yield  $60  ooo.  If 
the  rate  of  interest  received  in  this  fund  is  3  per  cent  and  it 
be  compounded  annually  the  annual  contribution  required  is 
$2220.  Accordingly  the  total  amount  to  be  raised  by  the 
additional  tax  is  $5220  per  annum,  and  this  is  at  the  rate  of 
nearly  1.5  mills  on  the  dollar.  The  annual  tax  rate  must, 
therefore,  be  raised  from  15  to  16.5  mills  on  the  dollar  for  a 
period  of  20  years  in  order  to  defray  the  cost  of  the  sewer- 
age system. 

Another  method  is  to  divide  the  cost  of  construction  into 
two  parts,  one  to  be  paid  by  a  general  tax  as  above  described, 
and  the  other  to  be  paid  by  an  assessment  on  the  property 
along  the  sewer  lines.  This  is  perhaps  a  fairer  plan,  for  those 
properties  which  do  not  front  on  the  sewer  lines  cannot  make 
connection  with  them  and  hence  do  not  receive  full  benefit. 
The  greatest  benefit  in  all  systems  of  drainage  and  sewerage 
is  to  the  community  at  large,  but  usually  some  people  receive 


60.  COST  AND  ASSESSMENTS. 

greater  advantages  than  others.  Property  along  a  sewered 
street  is  worth  more  than  property  on  an  unsewered  street, 
other  things  being  equal,  and  hence  it  is  fair  that  the  former 
should  pay  a  larger  proportion  of  the  cost  of  construction. 
As  to  what  this  proportion  should  be  opinions  and  practice 
greatly  vary,  and  each  town  must  be  left  to  decide  it  for  itself. 
When  a  special  assessment  is  laid  on  property  along  the 
sewer  lines  this  should  not  be  according  to  the  value  of  the 
property,  but  in  proportion  to  its  frontage,  the  idea  being 
that  the  advantage  of  being  able  to  connect  with  the  sewer 
increases  the  value  of  a  property  in  proportion  to  the  number 
of  houses  that  can  be  built  upon  it.  The  assessment  should 
be  the  same  along  branch  sewers  as  along  larger  ones,  and  a 
fair  plan  is  to  make  it  sufficiently  large  to  cover  the  cost  of 
the  smallest  lateral  sewers,  excluding  manholes,  catch  basins, 
and  flush  tanks.  On  this  plan  about  one-fourth  or  one-fifth 
of  the  cost  of  construction  is  paid  by  the  property  owners 
along  the  sewer  lines,  and  the  rest  is  provided  by  an  issue  of 
bonds,  for  whose  interest  and  redemption  a  uniform  annual 
tax  is  laid  on  all  assessed  property  for  a  number  of  years. 

In  towns  where  the  water  services  are  metered  and  both  the 
water  supply  and  sewer  systems  are  owned  by  the  municipality, 
it  seems  a  fairer  way  to  charge  such  a  rate  for  the  water  that  a 
portion  may  be  applied  each  to  the  water  works  and  sewer 
system,  as  the  use  of  the  sewer  is,  of  course,  directly  propor- 
tional to  the  amount  of  water  used.  No  towns  using  this 
method  are  known,  but  it  was  advocated  for  a  number  of  water 
supply  and  sewerage  systems  in  Porto  Rico.  The  use  of  meters, 
however,  met  with  such  violent  opposition  from  the  people, 
that  in  no  case  where  there  were  both  water  and  sewer  systems 
were  meters  installed.  It  is  interesting  to  note  that  while  the 
people  of  Porto  Rico  were  ready  and  anxious  to  vote  money 
for  a  good  water  supply  they  were,  in  general,  unwilling  to 
supply  any  means  for  disposing  of  the  wastes.  In  this  respect 


1?$  SEWERAGE   SYSTEMS.  IV. 

they  differ  not  at  all  from  the  smaller  communities  in  our  own 
country. 

The  future  growth  of  the  town  is  an  element  that  must 
always  be  considered  in  planning  a  sewerage  system.  The 
records  of  the  past  give  information  that  will  be  valuable  in 
the  estimation  of  increase  in  population  for  one  or  two 
decades,  but  beyond  this  all  estimates  will  be  merely  guesses. 
The  main  sewer  should  perhaps  be  made  large  enough  to  pro- 
vide for  the  probable  increase  in  population  for  the  period  of 
twenty  years,  but  further  than  this  it  is  not  wise  to  go.  If 
the  bonds  are  to  be  redeemed  in  twenty  years  the  community 
will  then  be  relieved  of  the  taxation  which  these  have  involved 
and  may  accordingly  make  enlargements  or  extensions.  In 
sanitary  matters  we  look  far  back  into  the  past  to  learn  the 
lessons  gathered  from  the  experience  of  our  ancestors,  the 
present  and  immediate  future  demand  of  us  most  active  work 
and  constant  vigilance,  but  the  problems  of  the  distant  future 
must  be  left  to  be  solved  by  posterity.  Avoiding  our  mis- 
takes and  building  upon  what  we  have  found  advantageous, 
posterity  shall  develop  more  perfect  sanitary  regulations  than 
now  are  known. 

61.   EXERCISES  AND  PROBLEMS. 

48.  Collect  facts  regarding  the  sewers  of  Paris,  their  early 
history,  and  the  systems  now  in  use. 

49  (a)  Consult  Gerhard's  House  Drainage  and  Sanitary  Plumbing 
(New  York,  1894),  and  describe  the  improved  bell  trap,  the  sanitas 
trap,  and  one  of  the  traps  having  a  mercury  seal. 

49  (b]  Inspect  the  plumbing  in  a  large  boarding  house  or  hotel, 
criticise  any  defects,  and  praise  its  good  points. 

49  (c)  Consult  Philbrick's  American   Sanitary  Engineering  (New 
York,  1881),  and  make  a  sketch  of  the  old  pan  closet  and  also  one 
of  a  grease  tank. 

50  (a)  Consult    Plumbing  and  House-drainage    Problems    (New 
York,  1892),  and  explain  a  few  of  the  common  defects  in  bath-room 
work  which  are  due  to  carelessness  of  plumbers. 


6l.  EXERCISES   AND    PROBLEMS.  179 

50  (b)  Read  an  article  by  Corser    in    Engineering  News,  Sept.   19, 
1891,  and  state  some  ideas  on  house  sewerage  from  an  architect's  point 
of  view. 

51  (a)  Consult  Bering's  article  in  Transactions  of  American  Society 
of  Civil  Engineers,  1881,  pp.  361-386,  and  give  an  abstract  of  his  com- 
parisons of  the  combined  and  separate  systems. 

51  (b)  Obtain  facts  regarding  the  new  sewerage  system  at  Baltimore, 
Md. 

52  (a)  Consult  Adams'  Sewers  and  Drains  (New  York,   1880),  and 
make  sketches  showing  arrangement  of  manholes  and  tidal  outlets. 

52  (b)  Consult  Baumeister's  Cleaning  and  Sewerage  of  Cities  (New 
York,  1894),  and  make  sketches  showing  European  styles  of  street 
basins. 

52  (c)  Consult   Engineering   Record  for   August    21,    1915,  and  find 
conclusions   regarding   comparisons   made   between   circular   and   egg- 
shaped  sewers. 

53  (a)  Consult   Staley  and  Pierson's  Separate  System  of  Sewerage 
(New  York,  1890),  and  make  sketches  of  a  fresh-air  inlet. 

53  (b)  Describe  the  action  of  one  of  the  mechanical  flush  tanks. 

53  (c)  Consult  OdelPs  article  on  the  Memphis  sewers  in  Transac- 
tions of  American  Society  of  Civil  Engineers  for  1881,  and  give  a  de- 
scription of  their  construction  and  operation. 

53  (d).  Consult  Engineering  Record  for  July  31,  1915,  and  ascertain 
facts  regarding  the  construction  of  a  large  storm  sewer  at  Los  Angeles, 
Calif. 

54  (a)  Determine  the  size  of  a  circular  sewer  to  carry  off  one  inch 
of  rainfall  per  hour  on  700  acres  when  the  fall  of  the  sewer  is  2  inches 
in  100  feet. 

54  (b)  Determine  the  size  of  a  circular  sewer  of  the  separate  system 
to  carry  the  sewage  of  25  ooo  people  when  the  fall  is  2  feet  in  i  mile. 

55  (a)  Consult  Waring's  Sewerage  and  Land  Drainage  (New  York, 
1889),  and  give  a  description  of  the  sewerage  system  at  Saratoga  Springs, 
N.  Y. 

55  (b)  Consult  Baumeister's  Cleaning  and  Sewerage  of  Cities  and 
ascertain  the  cost  of  concrete  sewers  in  European  cities. 

55  (c).  Consult  engineering  literature  and  obtain  facts  regarding  the 
improved  sewer  system  of  Havana,  Cuba. 


SEWERAGE  SYSTEMS.  IV. 

55  (d)  Consult  FolwelPs  Sewerage  (New  York,  1910),  and  read  his 
specifications  for  the  construction  of  a  sewerage  system. 

56  (a)  Consult  Latham's  Sanitary  Engineering  (London,   1875),  and 
give  an  account  of  methods  for  ventilating  sewers  by  windmills  and  by 
steam  jets. 

56  (6)  Consult  Transactions  of  American  Society  of  Civil  Engineers  for 
December,  1905,  and  obtain  facts  and  sketches  of  the  new  methods  em- 
ployed in  flushing  sewers  in  the  City  of  Mexico. 

57.  A  centrifugal  pump  is  to  lift  150000  gallons  of  sewage  per  hour 
through  a  height  of  12  feet,  the  suction  and  discharge  pipes  being  i  foot 
in  diameter  and  172  feet  long.     If  the  efficiency  of  the  pump  is  90  per  cent, 
estimate  the  horse-power  required. 

58.  Consult  Grey's  report  of   1884  on  the  sewerage  of  Providence, 
R.  I.,  and  give  a  fuller  description  of  the  operation  of  the  systems  of 
Liernur  and  Berlier. 

59.  Consult   Transactions   of   American   Society   of   Civil   Engineers 
for  December,   1892,   and  give  further  details  concerning  the  Shone 
system  in  American  cities. 

60  (a)  A  town,  whose  property  has  the  assessed  valuation  of  $7  325  ooo 
and  whose  annual  tax  rate  is  19  mills  on  $i,  issues  bonds  to  the  amount 
of  $225  ooo  to  build  a  sewerage  system,  these  being  at  4!  per  cent  interest 
and  maturing  in  1 5  years.  An  extra  tax  is  to  be  laid  to  meet  this  interest 
and  to  provide  a  sinking  fund  to  redeem  the  bonds,  the  rate  of  interest 
in  the  sinking  fund  being  3!  per  cent  compounded  annually.  How  many 
mills  must  be  added  to  the  tax  rate  for  this  purpose? 

60  (&)  A  city  builds  a  water  supply  system  costing  $125000  and  a 
sewer  system  costing  $75  ooo.     To  meet   this  expenditure  bonds  are 
issued  at  5  per  cent  and  maturing  in  20  years.     The  cost. of  operation 
and  maintenance  for  the  water  system  is  $6000  and  for  the  sewer  system 
$3000  per  annum.      All  water  services  are  metered,  the  population  of  the 
city  is  10  ooo  with   a  uniform   rate  of  increase  of  150  inhabitants  per 
year,  and  the  water  consumption  is  assumed  at  100  gallons  per  capita 
per  day.     What  rate  per  1000  gallons  of  water  must  the  consumer  pay 
in   order   to  amortize   the   debt  at  maturity?     Interest  on  the  sinking 
fund  is  at  4  per  cent,  compounded  annually.     What  proportion  of  the 
assessment    should   be  applied  to  the  water  supply  system   and  what 
proportion  to  the  sewer  system? 

6 1  (a)  What  is  the  distinction  between  a  deodorizer  and  a  disinfect- 


6l.  EXERCISES   AND   PROBLEMS.  1796 

ant?  What  is  a  germicide?  What  is  salt  glazing  and  slip  glazing  in 
earthenware  pipes?  What  sanitary  work  was  done  by  Hercules  under  con- 
tract with  King  Augeus? 

6 1  (b)  Consult  Fol well's  Sewerage  and  read  the  chapter  on  Practical 
Sewer  Construction. 

6 1  (c)  Consult  Transactions  of  American  Society  of  Civil  Engineers  for 
December,  1907,  and  read  the  report  of  the  committee  on  the  effect 
of  the  earthquake  on  the  sewers  of  San  Francisco. 

6 1  (d)  Consult  Engineering  News-Record,  Oct.  4,  1917,  and  describe 
the  large  reinforced  concrete  sewer  then  under  construction  at  Rich- 
mond, Va. 


180  DISPOSAL   OF    SEWAGE.  V. 


CHAPTER  V. 
DISPOSAL  OF  SEWAGE. 

62.    SEWAGE  AND  ITS  DECOMPOSITION. 

Sewage  is  water  containing  the  decaying  matter  of  house- 
hold wastes  in  suspension  and  solution,  and,  as  stated  in  the 
last  chapter,  the  weight  of  the  total  solids  is  always  much  less 
than  one  per  cent  of  the  whole.  European  sewage  has  the  total 
solids  from  1000  to  3000  parts  per  million,  but  in  American 
sewage,  owing  to  the  larger  volume  of  water  supply,  the  pro- 
portion is  generally  less  than  1000  and  often  as  low  as  500  parts 
per  million.  Of  the  solid  matter  about  two-thirds  is  organic, 
and  the  object  of  the  sewerage  system  is  to  remove  the  sewage 
from  the  town  before  the  decomposition  of  this  organic  matter 
has  fairly  begun. 

As  the  water  supply  flows  from  the  faucets  into  the  house 
fixtures,  air  becomes  mingled  with  it,  so  that  the  sewage  in  its  flow 
through  the  house  drains  contains  much  dissolved  oxygen. 
This  oxygen  immediately  attacks  'the  organic  matter,  and  the 
aerobic  bacteria  begin  their  useful  work  of  decomposition  and 
increase  in  number  and  activity.  As  the  oxygen  becomes  used 
up  in  this  process,  these  bacteria  decrease  in  number,  the  anaerobic 
bacteria  begin  their  work  and  the  decay  finally  goes  on  by  the 
process  of  putrefaction  in  which  the  organic  matter  is  decom- 
posed into  foul-smelling  gases  and  liquids.  Sewage,  therefore, 
presents  different  characteristics  at  different  stages  of  its  history. 

Fresh  sewage  is  that  flowing  from  the  house  drains  into  the 
sewers;  its  odor  is  not  bad,  and  the  decomposition  is  not  fairly 


62.  SEWAGE    AND   ITS    DECOMPOSITION.  l8l 

under  way.  Stale  sewage  is  that  about  one  day  old,  or  at  least 
of  such  an  age  that  the  odor  is  unpleasant.  Septic  sewage  is  so 
old  that  the  decomposition  is  of  the  putrefactive  kind  and  very 
ill-smelling  gases  are  evolved.  In  stale  sewage  the  aerobic 
bacteria  have  reached  their  highest  development,  in  respect  to 
both  number  and  activity,  while  in  septic  sewage  their  number 
is  low  compared  with  that  of  the  anaerobic  bacteria. 

The  following  analyses  of  the  Massachusetts  State  Board 
of  Health,  as  stated  by  Clark  in  1898,  give  an  idea  of  the  changes 
which  occur  in  sewage  from  the  fresh  to  the  septic  state,  the 
figures  being  in  parts  per  million: 

Fresh.  Stale.  Septic. 

Free  ammonia  26.0  45-Q  55  ° 

Albuminoid  ammonia  11.8  10.5  5.5 

Nitrogen  as  nitrites  0.21  o.o  o.o 

Nitrogen  as  nitrates  i.oo  o.o  o.o 

Oxygen  consumed  85.0  48.0  25.0 

Bacteria  per  cubic  centim  eter  i  950  ooo    3  800  ooo  500  ooo 

Here  it  is  seen  that  the  free  ammonia  increases  with  the  age 
of  the  sewage,  while  the  albuminoid  ammonia  and  the  amount 
of  oxygen  consumed  decrease.  In  septic  sewage,  therefore, 
a  considerable  proportion  of  the  organic  matter  has  become 
transformed  into  carbon  dioxide,  ammonia,  and  other  gases, 
but  no  nitrification  has  occurred,  and  in  fact  the  nitrites  and 
nitrates  of  the  fresh  sewage  appear  to  have  been  resolved  back 
into  ammonia. 

When  sewage  is  discharged  into  a  river,  this  is  usually  done 
during  the  stale  state  or  during  an  early  stage  of  that  state.  The 
river  water  then  furnishes  an  additional  supply  of  oxygen,  so  that 
decomposition  goes  on  by  means  of  nitrification  and  the  septic 
state  is  never  reached.  So  also  when  sewage  is  purified  by 
filtration  through  earth,  the  septic  state  is  not  reached.  Indeed, 
the  subject  of  septic  sewage  is  one  concerning  which  little  was 
known  prior  to  1895,  for  the  almost  universal  practice  had  been 


1 82  DISPOSAL   OF   SEWAGE.  V. 

to  dispose  of  sewage  as  quickly  as  possible  and  before  putrefaction 
had  begun.  Judging  from  the  number  of  bacteria,  stale  sewage 
is  more  dangerous  than  septic,  but  if  the  warning  given  by  the 
odor  is  of  any  value  the  septic  state  is  one  that  should  be  avoided, 
except  in  connection  with  a  properly  arranged  septic  tank. 

The  introduction  of  the  acid  wastes  of  factories  into  the 
sewers  is  not  regarded  as  desirable,  because  these  acids  are 
poisons  which  kill  the  useful  bacteria  of  fresh  sewage,  and  hence 
the  decomposition  may  proceed  by  the  septic  method  with  the 
result  of  giving  much  offense  by  the  foul  gases.  Such  acids, 
however,  are  usually  admitted  to  the  sewers,  and  as  a  consequence 
the  sewage  of  manufacturing  towns  has  a  very  complex  com- 
position and  is  more  liable  to  cause  river  pollution  than  the  sew- 
age from  houses. 

The  methods  for  the  disposal  of  sewage  are  now  to  be  taken 
up  and  discussed.  Its  disposal  in  streams  is  first  to  be  noted, 
and  then  chemical  precipitation,  filtration  through  sand-beds, 
utilization  on  farms,  purification  by  septic  tanks  and  contact  filters 
will  follow.  In  all  these  methods  the  end  to  be  constantly  kept 
in  view  is  to  resolve  the  organic  matter  into  harmless  constituents 
in  such  a  manner  that  neither  air  nor  water  may  suffer  pollution. 

63.    DISPOSAL  OF  SEWAGE  IN  RIVERS. 

When  a  brook  or  a  river  flows  through  a  village,  it  seems 
entirely  proper  to  the  inhabitants  to  throw  garbage  and  refuse 
into  it.  Privies  are  often  built  overhanging  it,  the  waste  of 
kitchens  is  turned  into  it,  and  rubbish  of  all  kinds  is  dumped 
upon  its  banks.  When  the  stream  is  a  mighty  river,  the  matter 
thrown  into  it  by  a  few  men  is  of  little  moment,  as  it  is  quickly 
diluted  and  oxidized  by  the  great  volume  of  water;  but  when 
the  stream  is  a  very  small  one,  it  becomes  fouled  so  as  to  be  more 
uncleanly  than  a  sewer.  The  village  itself  may  not  feel  the 
effect  of  this  pollution,  but  the  next  village  lower  down  on  the 
stream  may  be  seriously  affected  by  the  impure  water. 


63.  DISPOSAL   OF   SEWAGE  IN  RIVERS.  183 

An  impure  stream  becomes  purified  by  a  flow  of  sufficient 
length  if  additional  organic  matter  is  kept  out  of  it.  Aeration 
and  sedimentation  constantly  go  on,  and  by  these  processes 
impure  water  may  become  pure.  Hence  it  has  been  said  by 
some  that  a  flow  of  ten  miles  renders  sewage  harmless  in  a  river, 
while  a  British  commission  maintained  that  there  is  no  river 
in  England  or  Scotland  long  enough  to  effect  the  complete  puri- 
fication of  sewage.  It  is  recognized  by  all,  however,  that  a  small 
amount  of  sewage  in  a  large  river  will  soon  be  purified  so  as 
not  to  be  injurious,  and  that  a  large  amount  of  sewage  in  a  small 
river  cannot  be  purified.  Between  these  two  extremes  there  has 
been  held  every  variety  of  opinion  and  practice. 

It  has  been  shown  by  Mason  that  in  1890  germs  of  typhoid 
fever  were  carried  26  miles  by  the  Mohawk  and  Hudson  rivers, 
and  Sedgwick  has  also  shown  that  in  1802  such  germs  were  carried 
25  miles  by  the  Merrimac  River.  For  these  distances  at  least 
the  flow  of  the  river  did  not  effect  purification.  Negative  evidence 
indicating  that  no  disease  was  known  to  have  been  caused  by 
sewage  after  a  flow  of  four  or  five  miles  in  a  river  has  little  value 
in  comparison  with  a  few  positive  facts  like  these. 

The  amount  and  character  of  the  sewage,  the  volume  and 
velocity  of  flow  of  the  river,  and  the  kind  of  fishes  and  vege- 
tation found  in  it  are  three  controlling  factors  in  the  question 
of  river  pollution.  If  the  volume  of  sewage  is  larger  than  one- 
twentieth  of  the  river  water,  or  if  it  contains  acids  of  manufac- 
tories, the  conditions  are  very  unfavorable  for  its  purification. 
If  the  velocity  of  the  stream  is  small  and  there  are  no  fishes 
or  vegetation  in  it,  the  conditions  are  also  unfavorable.  Fishes 
eat  the  grosser  particles  of  organic  matter  and  vegetable  growths 
absorb  the  dissolved  matter,  but  the  acid  wastes  of  factories  may 
kill  both  fishes  and  vegetables  as  well  as  the  bacteria  of  the 
sewage  and  hence  retard  the  purification.  When  a  river  is 
sluggish  the  available  oxygen  is  soon  used  up  by  the  sewage 
and  the  septic  state  of  putrefaction  may  ensue.  Leeds  reports 
that  when  the  Schuylkill  River  near  Philadelphia  was  frozen 


1 84  DISPOSAL   OF   SEWAGE.  V. 

over  in  1883,  the  gaseous  products  of  this  putrefaction  were 
so  abundant  as  to  escape  through  holes  in  the  ice,  and  when 
ignited,  the  flames  rose  a  foot  in  height. 

By  far  the  larger  number  of  American  cities  turn  their  sew- 
age into  rivers  or  into  the  ocean.  The  disposal  at  sea  is  com- 
paratively unobjectionable  if  the  discharge  is  made  at  such 
times  that  it  will  not  be  returned  to  the  shore  by  the  tides,  but 
this  cannot  always  be  secured.  The  disposal  by  discharge  into 
a  river  is  now  universally  regarded  as  a  menace,  if  not  an  actual 
danger,  to  towns  which  take  their  water  supply  at  points  below, 
and  laws  have  been  enacted  in  some  states  to  prevent  the  con- 
tamination of  rivers.  These  laws  are  necessarily  general  in  their 
wording,  and  the  specific  details  are  left  to  be  supplied  in  each 
case  by  the  boards  of  health.  For  instance,  the  law  may  forbid 
any  person  to  put  "any  polluting  matter  into  a  stream  used  as 
a  source  of  water  supply,"  but  it  must  be  left  to  the  board  of 
health  to  determine  whether  the  sewage  of  a  village  is  or  is  not 
polluting  matter. 

As  a  consequence  of  these  laws,  many  towns  and  cities  have 
been,  or  will  soon  be,  obliged  to  install  plants  for  the  purification 
of  their  sewage.  These  plants  do  not  render  the  sewage  so  pure 
that  it  is  safe  for  drinking,  but  they  can  generally  make  it  as  free 
from  bacteria  as  the  water  of  the  river  into  which  it  is  to  be  dis- 
charged. The  degree  of  purity  required  by  the  boards  of  health 
will  depend  upon  the  relative  volumes  of  the  sewage  and  river 
flow  and  the  distance  to  the  next  town  which  takes  its  water  supply 
from  the  river.  The  criterion  of  a  certain  number  of  bacteria 
per  cubic  centimeter  is  often  adopted,  and  an  additional  one  is 
that  of  the  organic  matter  remaining  after  purification.  If  the 
river  water  contains  3000  bacteria  per  cubic  centimeter  and  the 
purified  sewage  only  2000,  and  if  the  amount  of  organic  matter 
is  about  the  same  in  both,  it  would  seem  that  the  artificial  puri- 
fication has  been  carried  as  far  as  practically  necessary  The 
bacterial  examinations  should  also  extend  to  the  determination 


64.  SCREENING    OF   SEWAGE.  185 

of  the  relative  number  of  Bacillus  coli  communis  and  allied 
species  in  the  water  and  sewage.  These  requirements  and  the 
methods  for  enforcing  them  are  as  yet  not  fully  developed,  but 
the  guiding  principles  have  been  well  established,  and  the  time 
is  near  at  hand  when  they  will  certainly  become  a  powerful 
factor  in  the  progress  of  sanitary  science. 

64.    SCREENING  OF  SEWAGE. 

A  screen  or  sieve  may  be  used  to  effect  a  slight  degree  of 
purification  in  sewage  by  intercepting  a  part  of  the  suspended 
organic  matter.  By  passing  the  sewage  through  several  sieves, 
each  finer  than  the  preceding  one,  a  large  proportion  of  the  sus- 
pended matter  may  be  removed  and  the  sewage  be  rendered 
much  clearer  in  appearance.  A  sieve,  however,  does  not  remove 
the  dissolved  organic  matter,  and  this  is  usually  the  part  which 
is  in  the  state  of  most  active  decay  and  hence  the  most  dangerous. 

Sewage  must  be  screened  to  a  certain  degree  whenever  it 
is  pumped  or  whenever  it  is  distributed  over  filter  beds.  A 
single  box  screen  at  the  end  of  the  sewer  will  catch  the  rags 
and  sticks  and  thus  render  the  sewage  clear  enough  to  be  pumped, 
but  for  distribution  on  filter  beds  a  series  of  screens  should  be 
used.  For  this  purpose  the  sewage  may  be  led  into  an  open 
masonry  channel  of  rectangular  section  in  which  vertical  screens 
or  sieves  are  placed  at  intervals ;  if  the  velocity  of  flow  is  small, 
some  sedimentation  will  also  occur.  After  a  day  or  two  the 
matter  accumulated  at  the  screens  may  be  removed;  this  may 
be  digested  or  burned  like  garbage,  or  if  such  methods  are  not 
available,  it  may  be  mixed  with  sawdust  and  then  be  spread 
upon  the  fields  to  serve  as  manure. 

Screening  through  coke  is  a  process  which  has  received  much 
attention.  Coke  is  the  porous  charcoal  obtained  by  heating 
bituminous  coal  in  the  absence  of  air.  When  sewage  is  passed 
through  it,  the  suspended  matter  is  strained  out,  but  this  accu- 
mulates in  the  coke  and  after  a  week  or  more  a  new  supply  is 


l86  DISPOSAL  OF  SEWAGE.  V. 

needed.  The  coke  is  spread  in  a  bed  about  a  foot  thick  sup- 
ported on  wire  screens,  and  the  sewage  is  passed  through  it  by 
the  action  of  gravity.  The  effect  of  the  screening  will  vary 
with  the  kind  of  coke  and  the  rate  of  passage  through  it,  but 
from  40  to  60  per  cent  of  the  organic  matter  can  be  generally 
removed.  When  the  coke  becomes  clogged  it  is  removed  and 
burned  under  boilers,  but  this  often  gives  offensive  odors,  and 
hence  the  plan  of  first  heating  it  in  an  oven  to  extract  the  grease 
has  been  tried. 

When  a  bed  of  coke  is  thick  and  the  rate  of  passage  of 
the  sewage  is  slow,  the  process  becomes  filtration  instead  of 
screening,  for  thus  the  bacteria  are  given  time  to  do  their  use- 
ful work  on  the  dissolved  organic  matter.  Ashes,  cinders,  peat, 
and  similar  substances  have  been  used  instead  of  coke  for  such 
beds,  and  usually  the  action  which  results  is  a  combination  of 
screening  and  filtration.  The  process  of  screening  alone  may 
be  carried  on  continuously,  but  the  process  of  filtration  should 
be  intermittent  in  order  that  air  may  enter  the  beds  and  furnish 
oxygen  to  the  bacteria.  In  screening  processes  the  bacteria 
are  decreased  in  number  merely  because  the  amount  of  decaying 
organic  matter  is  decreased,  but  in  true  filtration  processes  the 
bacteria  are  almost  entirely  removed  because  their  work  is  done, 
the  organic  matter  having  been  totally  decomposed  and  purified. 
In  all  screening  methods  it  is  desirable  that  the  sewage  should 
be  as  fresh  as  possible  in  order  to  avoid  the  offense  which  might 
be  caused  by  foul  organic  matter. 

Screening  chambers  for  the  removal  of  grit  and  coarse  organic 
matter  are  also  used  when  sewage  is  stored  in  basins  either  -  for 
the  purpose  of  chemical  precipitation  or  for  septic  treatment. 
Such  settling  basins  are  also  used  to  receive  sewage  before 
it  is  distributed  upon  filter  beds,  for  it  has  been  found  that  it 
is  desirable  that  the  sewage  should  have  reached  the  stale  stage 
before  it  is  applied  to  the  beds.  In  these  settling  basins  sludge 
accumulates  at  the  bottom  and  arrangements  must  be  made 


65.  AERATION   OF    SEWAGE.  187 

for  periodically  removing  it.  The  term  plain  sedimentation 
refers  to  these  and  other  cases  in  which  the  sewage  has  not 
reached  the  septic  state. 

65.   AERATION  OF  SEWAGE. 

The  aeration  of  sewage  consists  in  supplying  it  with  air,  so 
that  oxygen  may  be  furnished  to  the  aerobic  bacteria  and  enable 
them  to  continue  the  useful  work  of  purification.  Aeration  is 
always  beneficial  in  removing  odors,  and  effective  purification 
will  result  if  sufficient  air  is  furnished  during  a  considerable 
period  of  time.  It  must  not  be  forgotten  that  aerobic  bacteria 
require  both  time  and  oxygen  for  the  performance  of  their  func- 
tions, and  hence  it  is  plain  that  one  violent  aeration  of  short 
duration  will  not  be  as  effective  as  a  number  of  aerations  of  less 
intensity.  In  all  methods  of  aeration  it  is  best  that  the  sewage 
should  first  be  screened  in  order  that  the  effect  of  the  oxygen 
may  be  concentrated  upon  the  organic  matter  in  solution. 

When  sewage  is  filtered  through  land  by  the  method  of  in- 
termittent filtration  (Art.  67)  or  broad  irrigation  (Art.  68),  it 
usually  reaches  the  beds  in  the  stale  stage  and  it  is  then  desirable 
that  it  should  receive  a  liberal  supply  cf  air  in  order  that  the 
aerobic  bacteria  may  continue  their  useful  work.  In  the  opera- 
tion of  the  sprinkling  filters  described  in  Art.  71,  the  sewage 
is  distributed  upon  the  beds  in  a  spray  for  the  purpose  of 
introducing  oxygen  to  enable  the  aerobic  bacteria  to  properly 
act  upon  the  organic  matter  and  resolve  it  into  harmless  forms. 

Combined  screening  and  aeration  may  be  done  for  a  small 
volume  of  sewage  by  the  use  of  a  number  of  horizontal  sieves, 
one  placed  above  the  other  and  the  finest  being  at  the  bottom. 
As  the  sewage  falls  through  the  intervals  between  the  sieves 
it  becomes  aerated  more  and  more,  and  after  passing  the  last 
sieve  the  suspended  matter  is  in  large  part  removed  and  the 
bacteria  are  actively  at  work  on  the  dissolved  matter.  This 
method  generally  requires  the  sewage  to  be  pumped,  but  the 


1 88  DISPOSAL  OF   SEWAGE.  V 

expense  of  pumping  has  prevented  the  method  from  coming  into 
use  much  further  than  the  experimental  stage.  Artificial  aera- 
tion by  agitating  the  'sewage  with  revolving  wheels  and  by  blow- 
ing air  into  it  has  likewise  been  tried,  but  this  is  also  expensive 
and  can  be  used  only  on  a  small  scale.  The  sewage  filtration 
plant  at  Reading,  Pa.,  consists  of  a  double  system  of  beds,  one 
about  12  feet  above  the  other;  after  passing  through  the  upper 
beds  the  sewage  falls  in  drops  to  the  lower  ones,  and  thus  is 
effectively  aerated. 

It  is  seen  by  the  above  discussions  that  screening  and  aera- 
tion, either  separately  or  combined,  do  not  constitute  a  method 
for  the  effective  purification  of  sewage  except  in  unusual  special 
cases  where  the  volume  to  be  treated  is  small.  They  are,  how- 
ever, valuable  adjuncts  in  all  the  systems  of  sewage  disposal 
which  are  to  be  described  in  the  following  articles.  By  the 
proper  use  of  these  systems  it  is  possible  to  bring  ordinary  sewage 
to  any  desired  degree  of  purification. 

66.    CHEMICAL  PRECIPITATION. 

The  theory  of  the  precipitation  of  sewage  by  means  of  chemicals 
is  the  same  as  that  given  in  Art.  25  for  water.  The  chemical  sub- 
stances are  added  in  the  form  of  a  solution,  and  their  reaction 
results  in  a  precipitate  which  falls  by  the  action  of  gravity  and 
drags  down  with  it  the  suspended  organic  matter  of  the  sewage. 

Lime,  or  calcium  monoxide  (CaO),  when  placed  in  water 
forms  calcium  hydrate  (CaO,H2O),  and  this  solution  when 
added  to  sewage  containing  carbon  dioxide  (CO 2)  results  in 
the  formation  of  calcium  carbonate  (CaCO3),  which  is  heavier 
than  water  and  hence  precipitates.  The  amount  of  lime  added 
to  the  sewage  averages  about  200  parts  per  million,  or  about 
1600  pounds  of  lime  to  i  ooo  ooo  gallons  of  sewage.  As  decaying 
organic  matter  gives  off  carbon  dioxide,  this  is  always  found  in 
sewage,  and  sufficient  lime  should  be  added  to  completely  absorb 
it,  if  the  best  results  are  to  be  obtained. 


66.  CHEMICAL    PRECIPITATION.  189 

Alum,  an  aluminum- potassium  sulphate,  is  a  precipitant 
much  quicker  in  action  than  lime,  the  substance  thrown  down 
being  aluminum  hydrate,  according  to  the  reaction  given  in 
Art.  25.  The  quantity  of  alum  required  is  only  about  one-half 
of  that  of  lime,  but  its  cost  is  about  three  times  as  great.  Accor,d- 
ingly  a  mixture  of  lime  and  alum  is  frequently  employed  in  the 
proportion  of  about  one  part  of  the  former  to  four  parts  of  the 
latter. 

Copperas,  or  ferrous  sulphate  (FeO,SO3,yH2O),  and  ferric 
sulphate  (Fe2O3,3SOs),  are  also  used  for  clarifying  sewage,  the 
latter  in  particular  forming  a  ferric  hydroxide  (Fe(OH)3)  which 
is  very  quickly  precipitated.  Copperas  generally  requires  the 
addition  of  lime  in  order  to  make  it  efficient,  and  the  precipi- 
tated substance  is  a  ferrous  hydrate  (Fe(OH)2)  or  a  ferrous 
carbonate  (FeCOs).  It  cannot  be  said,  however,  that  either 
of  these  precipitants  is  always  more  efficient  than  alum  or  lime, 
for  it  is  found  that  different  kinds  of  sewage  require  different 
treatment,  and  in  each  case  some  experimenting  is  necessary 
to  determine  the  most  advantageous  and  economical  chemicals.  ' 

By  chemical  treatment  a  large  part  of  the  suspended  organic 
matter  and  about  one-fourth  of  the  dissolved  organic  matter 
may  be  removed  from  sewage.  The  matter  precipitated  in  the 
bottom  of  the  tanks  is  called  sludge,  while  the  purified  sewage 
is  generally  termed  the  effluent.  The  action  of  the  chemicals 
also  greatly  reduces  the  number  of  bacteria,  those  not  precipitated 
in  the  sludge  being  poisoned,  so  that  under  very  careful  treat- 
ment the  effluent  may  contain  less  than  five  per  cent  of  the 
bacteria  of  the  original  sewage.  Hence  the  effluent  is  so  far 
purified  that  in  many  cases  it  can  be  turned  into  rivers  with- 
out fear  of  causing  pollution. 

A  precipitating  basin  is  often  formed  by  an  open  conduit 
with  a  very  slight  slope  which  is  built  of  concrete  and  has  gates 
to  regulate  the  flow.  In  the  figure  the  plan  of  such  a  conduit 
is  shown,  its  width  being  about  5  feet,  its  depth  3  feet,  and  its 


I QO  DISPOSAL    OF    SEWAGE.  V 

length  200  feet,  the  capacity  being  sufficient  to  treat  the  sewage 
of  about  1000  people.  The  sewage  enters  at  A,  either  from  the 
sewer  or  from  a  pump  which  has  raised  it  to  the  required  eleva- 


ol 


D 


D  D 


D 


PRECIPITATING  CONDUIT. 

tion,  and  passes  out  at  V.  The  chemicals  are  in  solution  in  the 
tanks  C,  from  which  they  flow  directly  into  the  conduit,  and  the 
gates  D  regulate  the  flow.  EE  are  tracks  where  a  wagon  runs 
when  carrying  away  the  sludge,  this  operation  being  done  about 
twice  a  week.  A  duplicate  conduit  is  usually  provided,  so  that 
when  one  is  being  cleaned  the  other  may  be  in  operation. 

The  intermittent  method  of  operating  a  precipitating  basin 
is  to  fill  it  with  sewage,  then  to  add  the  chemicals,  and  after 
the  contents  have  stood  for  a  few  hours  to  discharge  the  liquid 
portion,  the  sludge  accumulating  during  several  such  fillings. 
The  continuous  method  consists  in  keeping  the  basin  nearly 
full  and  allowing  the  effluent  to  flow  out  as  fast  as  the  crude 
sewage  enters,  the  chemicals  being  continually  added.  Ex- 
perience indicates  that  the  continuous  method  is. the  better  one, 
but  care  is  required  in  both  methods  that  the  final  discharge  be 
not  made  so  rapidly  as  to  cause  the  soft  sludge  to  mingle  again 
with  the  effluent. 

Vertical  tanks  are  used  more  extensively  than  conduit,  basins 
when  a  large  volume  of  sewage  is  to  be  treated,  as  they  occupy 
less  space  and  the  sludge  is  spread  over  a  smaller  area.  Such 
a  tank  may  be  a  masonry  basin  when  the  ground  is  low  below 


66. 


CHEMICAL    PRECIPITATION. 


the  main  sewer  outlet  so  that  an  excavation  can  be  made,  or 
it  may  be  made  of  riveted  steel  plates  and  be  placed  above  ground 
when  the  sewage  is  to  be  pumped.  In  the  figure  the  first  diagram 
shows  a  masonry  tank  where  the  sewage  enters  by  a  conduit 


PRECIPITATING  TANKS. 

at  A,  whence  it  falls  to  D  and  then  rises  to  flow  away  at  B\  the 
soft  sludge  is  removed  from  the  bottom  by  means  of  a  pump 
attached  to  the  pipe  C.  The  second  diagram  shows  an  elevated 
steel  tank  where  the  sewage  is  pumped  up  to  A,  whence  it  falls 
through  the  vertical  pipe  AD  and  the  effluent  passes  out  at  B, 
while,  as  before,  the  sludge  is  pumped  out  through  C.  In  both 
cases  the  operation  is  continuous,  the  dissolved  chemicals  being 
constantly  added  to  the  crude  sewage  as  it  enters. 

The  disposal  of  the  sludge  is  the  most  difficult  part  of  the 
problem,  for  this  is  merely  soft  mud  when  it  is  taken  from  the 
basins.  Sometimes  shavings,  peat,  or  leaves  are  mixed  with 
the  sludge,  so  as  to  enable  it  to  be  more  easily  handled,  and  it 
is  then  burned  or  spread  upon  the  fields.  Sometimes  it  is  run 
into  scows  and  dumped  at  sea.  For  a  large  plant  the  most 
advantageous  way  seems  to  be  to  run  the  soft  sludge  into  an 
apparatus  called  a  filter  press,  which  squeezes  out  the  liquid 
portion  and  forms  the  solid  portion  into  cakes.  The  liquid 
is  run  back  into  the  tanks  to  be  again  precipitated,  while  the 
cakes  are  buried  in  the  ground  or  burned  in  a  garbage  crematory. 
The  cakes  have  no  value  for  manure,  as  the  precipitate  is  in 
large  part  mineral  matter  from  the  chemicals;  ,when  the  soft 
sludge  is  mixed  with  sawdust  or  compost  the  compound  formed 


DISPOSAL  OF   SEWAGE.  V. 

may  have  a  slight  value,  but  usually  not  enough  to  induce  farmers 
to  cart  it  away. 

This  method  of  sewage  disposal  has  been  much  used  in  Europe, 
and  since  1890  has  been  introduced  in  a  number  of  American 
towns  and  cities.  In  1893  a  large  installation  of  the  system 
was  made  at  the  Columbian  Exposition  in  Chicago,  where  the 
sewage  collected  by  the  Shone  system  was  forced  to  a  vertical 
pipe  30  inches  in  diameter,  around  which  four  precipitating 
tanks  were  placed  of  the  general  style  shown  in  the  second  diagram 
of  the  above  figure.  Each  tank  was  32  feet  in  diameter  at  the 
top  and  the  height  of  the  straight  sides  was  32  feet  also,  the 
combined  capacity  of  the  four  tanks  being  237  ooo  gallons.  The 
effluent  was  run  into  Lake  Michigan,  while  the  sludge  was  pressed 
into  cakes  which  were  burned  in  the  garbage  crematory. 

The  effluent  from  a  chemical  precipitation  plant,  although 
much  clearer  and  purer  than  the  sewage,  is  far  from  being  like 
pure  water.  The  sewage  has  about  40  per  cent  of  the  organic 
matter  in  suspension  and  60  per  cent  in  solution,  and  if  all  of 
the  former  and  one-fourth  of  the  latter  be  removed  there  still 
remains  in  the  effluent  45  per  cent  of  the  original  organic  matter. 
While  the  bacteria  have  been  reduced  in  number,  owing  to  the 
poisonous  action  of  the  chemicals,  the  amount  of  organic  matter 
remaining  in  the  effluent  is  still  high,  and  hence  the  remaining 
bacteria  may  increase  and  multiply  as  soon  as  the  effluent  is 
run  into  a  stream  where  oxygen  can  be  furnished  to  it. 

The  largest  chemical  precipitation  plant  in  the  United  States  is 
that  at  Worcester,  Mass.,  which  was  started  in  1890.  The 
sewage  first  passes  through  a  screening  chamber,  where  a  large 
part  of  the  grit  and  coarse  organic  matter  is  removed,  and  then 
passes  into  conduits  where  lime  is  added  to.  cause  precipitation. 
These  conduits  lead  to  settling  basins  which  are  66  X 100  feet  in 
size,  and  after  the  precipitation  is  completed  the  effluent  passes 
on  either  to  the  river  or  to  filtration  beds.  In  1905  the  average 
amount  of  sewage  treated  daily  was  10  no  ooo  gallons,  of  which 


66.  CHEMICAL   PRECIPITATION.  193 

8  930  ooo  gallons  were  turned  into  the  Blackstone  River  and  the  re- 
mainder further  purified  by  filtration  through  sand  beds.  The  wet 
sludge  from  the  bottom  of  the  settling  basins  is  pumped  to  the 
presses,  lime  being  again  added  before  pressing;  in  1905  the  aver- 
age amount  of  wet  sludge  pressed  per  day  was  45  070  gallons,  from 
which  53  tons  of  dry  sludge  cake  were  produced.  The  cost  of 
the  precipitation  was  $5.56  and  that  of  the  sludge  disposal  $6.33 
per  million  gallons  of  sewage,  or  about  38  cents  per  year  for  each 
person  on  the  sewage  system.  Chemical  analyses  of  the  sewage 
and  effluent  showed  that  the  total  amount  of  organic  matter 
removed  was  51.5  per  cent  as  measured  by  albuminoid  ammonia 
and  22.9  per  cent  as  measured  by  the  volatile  part  of  the  residue 
on  evaporation.  The  sewage  of  Worcester  contains  much  iron 
from  wire  mills,  and  of  this  63.2  per  cent  was  removed. 

Opinions  differ  as  to  the  efficiency  of  different  kinds  of  chemicals, 
and  doubtless  this  depends  upon  the  character  of  the  sewage. 
Experiments  by  Hazen  in  1889  showed  that  under  good  condi- 
tions alum  removed  91  per  cent  of  the  bacteria,  ferric  sulphate 
removed  95  per  cent,  lime  removed  97  per  cent,  and  lime  with 
copperas  removed  97  per  cent.  With  respect  to  the  dissolved 
organic  matter  he  found  that  ferric  sulphate  removed  less  than 
one-half,  while  lime  removed  less  than  one-fifth.  On  the  other 
hand  experiments  made  by  Johnson  at  Columbus,  O.,  in  1905, 
showed  that  the  number  of  bacteria  increased  in  a  tank  where 
lime  and  copperas  were  used,  while  42  per  cent  were  removed  in 
a  tank  where  alum  was  employed. 

Some  chemical  precipitation  plants  have  been  abandoned  after 
a  few  years'  service  on  account  of  the  high  cost  of  operation  or 
the  imperfect  purification  of  the  effluent.  Notwithstanding  the 
extensive  use  of  this  method  in  Europe,  it  does  not  seem  likely 
that  it  is  destined  to  become  widely  employed  in  the  United 
States,  the  general  tendency  here  being  towards  the  methods 
which  will  be  described  in  the  following  articles. 


1 94  DISPOSAL  OF  SEWAGE.  V. 

67.    INTERMITTENT  FILTRATION. 

The  method  of  purifying  sewage  by  filtration  is  founded  on 
the  same  principles  as  those  set  forth  in  Art.  28  for  the  artificial 
filtration  of  water.  Sewage  is  a  very  impure  water,  but  not 
much  more  impure  than  the  surface  drainage  of  some  pastures 
and  swamps;  by  passing  it  through  soil  at  a  slow  rate  and  sup- 
plying sufficient  air  to  enable  the  aerobic  bacteria  to  work,  the 
dead  organic  matter  becomes  completely  changed  into  harmless 
gases  and  mineral  compounds,  so  that  the  resulting  effluent  is 
clear  and  pure  water. 

In  the  filtration  of  a  water  supply,  either  the  continuous  or 
the  intermittent  method  may  be  used,  but  with  sewage  the  inter- 
mittent method  of  operation  is  more  generally  employed,  because 
its  larger  proportion  of  organic  matter  requires  the  presence  of 
a  greater  amount  of  air.  When  a  filter  bed  is  drained  of  its 
liquid  contents,  the  surfaces  of  the  sand  grains  remain  still  covered 
with  thin  films  of  water,  and  the  air  of  the  atmosphere  enters 
around  these  films  and  thus  furnishes  oxygen  to  the  bacteria 
which  are  engaged  in  hastening  the  chemical  operations  of 
oxidation  and  nitrification. 

In  water  filtration  the  greater  part  of  the  bacteria  are  at  work 
in  the  top  of  the  layer  of  sand,  but  it  has  been  the  aim  in  con- 
structing filter  beds  for  sewage  to  extend  their  operation  further 
downward.  This  has  been  done  by  using  coarser  materials, 
such  as  gravel,  broken  stone,  and  cinders,  so  as  to  prevent  the 
clogging  which  results  from  fine  sand.  A  portion  of  the  sludge 
collects  upon  the  surface,  however,  and  from  time  to  time  it  is 
necessary  that  this  be  removed  and  fresh  sand  be  added,  as  in 
water  filtration. 

The  rate  of  filtration  of  sewage  must  be  slower  than  that  of 
water,  and  hence  a  larger  area  is  required  for  a  given  volume  than 
in  water  purification.  The  rates  for  water  range  from  2  ooo  ooo 
to  5  oooooo  gallons  per  acre  per  day,  but  for  sewage  the  rate 
may  be  as  low  as  50000  or  100000  gallons  per  acre  per  day. 


67  INTERMITTENT    FILTRATION.  1 95 

As  a  very  rough  rule,  one  acre  will  purify  the  water  supply  for 
a  city  of  20  ooo  people  or  more,  but  it  will  scarcely  be  sufficient 
for  the  sewage  of  1000  people. 

The  most  favorable  location  for  sewage  filter  beds  is  along 
the  bank  of  the  stream  into  which  the  effluent  is  to  be  discharged. 
The  average  size  of  the  beds  is  about  one  acre,  and  each  of  these 
has  its  own  main  underdrain,  into  which  the  smaller  lateral 
drains  lead.  It  is  generally  too  expensive  to  build  masonry 
walls  to  separate  the  beds,  and  hence  wide  earthen  embankments 
are  made,  these  being  thoroughly  rolled.  The  bottoms  of  the 
beds  are  usually  natural  earth,  in  which  the  underdrains  are 
laid  in  trenches.  These  drains  are  provided  with  valves  at  the 
places  where  they  pass  through  the  embankments,  and  by  means 
of  these  the  rate  of  filtration  is  regulated.  When  the  soil  is  of 
favorable  quality  the  expense  of  preparation  of  a  series  of -beds 
may  be  as  low  as  $2000  per  acre,  so  that  the  entire  sewage-filter- 
ing field  for  a  city,  notwithstanding  its  larger  area,  may  cost 
less  than  the  filter  beds  for  the  water  supply.  A  sedimentation 
basin  is  not  needed,  because  the  effluent  is  not  to  be  used,  but  a 
receiving  basin  for  the  crude  sewage  is  necessary  so  as  to  properly 
distribute  it  over  the  different  beds. 

It  has  been  found  that  fresh  sewage  requires  a  slower  rate 
of  filtration  than  stale  sewage.  This  is  due  to  the  circumstance 
that  time  is  required  to  develop  the  full  number  of  bacteria  needed 
to  perform  the  work  of  oxidation  and  nitrification.  In  stale 
sewage  the  bacteria  have  reached  their  maximum  development 
and  hence  its  purification  takes  place  more  rapidly  in  the  filtering 
material  than  does  that  of  fresh  sewage,  while  less  sludge  is  also 
deposited  on  the  surface.  Septic  sewage  is  also  filtered  through 
sand  beds;  the  amount  of  sludge  in  this  case  is  smaller,  because 
some  of  it  has  been  changed  into  gas,  but  the  bad  odors  evolved 
in  the  storage  and  application  of  sewage  in  this  form  are  objec- 
tionable, although  these  may  be  partially  obviated  by  effective 
aeration. 


196  DISPOSAL   OF   SEWAGE.  V. 

The  frequency  of  draining  and  aeration  will  depend  upon 
the  rate  of  .filtration  and  upon  the  degree  of  purity  required 
in  the  effluent  as  well  as  upon  the  character  of  sewage  and 
filtering  material,  and  is  to  be  determined  in  each  case  by  ex- 
periment. For  a  very  small  volume  of  sewage  a  method  of 
forced  aeration  has  been  advocated  and  tried;  here  the  small 
beds  are  supported  in  boxes  with  a  sieve  bottom  and  air  is  blown 
through  them  by  a  pump  after  they  have  been  drained. 

The  frequency  of  cleaning  the  surface  depends  also  upon 
the  character  of  the  sewage  and  the  rate  of  nitration,  and  the 
aim  should  be  to  render  the  intervals  as  long  as  possible.  In 
general  a  period  of  two  or  three  months  elapses  between  the 
times  of  cleaning,  but  the  most  perfect  filtration  would  be  like 
that  which  occurs  in  nature,  where  the  surface  requires  no  clean- 
ing. In  nature  this  is  usually  effected  through  the  absorption 
of  the  organic  matter  by  growing  plants,  and  the  artificial  appli- 
cation of  this  process  to  sewage  leads  to  the  method  of  irrigation 
which  is  to  be  discussed  in  the  next  article. 

With  proper  attention  sewage  can  be  purified  by  intermittent 
filtration  so  that  the  effluent  is  undistinguishable  from  pure  water 
by  either  chemical  or  biological  analyses.  The  organic  matter 
has  been  transformed  into  carbon  dioxide  and  ammonia,  the 
ammonia  has  combined  with  the  mineral  substances  in  the  soil 
to  form  nitrates,  and  the  bacteria  have  been  reduced  to  a  number 
fewer  than  is  found  in  natural  potable  waters.  Sentiment,  of 
course,  forbids  the  use  of  the  effluent  as  drinking  water,  ,but 
there  is  no  scientific  reason  why  it  may  not  be  used  as  such  with 
entire  safety  if  comprehensive  analyses  and  their  interpretations 
so  indicate.  Chlorine  is  not  removed  by  filtration,  and  the 
amount  of  this  in  the  effluent  will  hence  be  found  very  high,  but 
this  has  no  bad  influence  on  health,  and  its  presence  has  a  wholly 
different  interpretation  from  that  of  a  similar  quantity  found  in 
the  natural  waters  of  the  neighborhood.  The  following  analyses 
"of  sewage  and  its  effluent  from  one  of  the  experimental  tanks  of 


67.  INTERMITTENT   FILTRATION.  IQ7 

the  State  Board   of  Health  of  Massachusetts  will  give  a  typical 
idea  of  the  results  of  intermittent  nitration: 

Sewage.  Effluent. 

Total  solids,                     parts  per  million  466.8  214.4 

Inorganic  matter,    "        "        "  338.0  202  7 

Organic  matter,       "        "       "  128.8  11.7 

Chlorine,                            "        "        "  38-6  38.1 

Free  ammonia,                  "        "       "  17.111  0.050 

Albuminoid  ammonia       "        "       "  4-389  0079 

Nitrogen  as  nitrates,          "        *        "  o.no  9.220 

Nitrogen  as  nitrites,          "        "        "  o.on  0.005 

Bacteria,  number  per  cubic  centimeter  633  ooo  120 

Chemical  precipitation  and  filter  beds  have  been  combined 
in  order  to  reduce  the  area  required  for  the  beds  or  to  increase 
the  rate  of  nitration.  When  the  chemical  precipitation  destroys 
a  high  percentage  of  the  bacteria,  it  seems  desirable  that  the 
effluent  from  the  precipitation  tanks  should  be  aerated  or  be 
stored  in  basins  for  a  sufficient  length  of  time  to  enable  the  bacteria 
to  increase  to  such  numbers  that  they  may  do  effective  work  in 
continuing  the  purification  in  the  filter  beds.  Although  this 
combination  of  methods  has  been  tried  in  a  number  of  towns, 
final  deductions  are  lacking  as  to  its  economy  and  comparative 
efficiency,  but  the  general  tendency  is  not  toward  chemical  pre- 
cipitation as  a  preparation  for  filtration.  The  works  at  East 
Orange,  N.  J.,  which  were  of  this  kind,  were  abandoned  after 
a  few  years  of  use  on  account  of  the  expense  involved.  At 
Worcester,  Mass.,  in  1905,  about  12  per  cent  of  the  chemically 
treated  sewage  was  further  purified  by  flow  through  sand  beds, 
as  also  was  a  slightly  larger  amount  of  untreated  sewage.  The 
cost  of  the  chemical  precipitation  and  subsequent  filtration  was 
$16.95  per  million  gallons,  while  that  of  the  filtration  of  untreated 
sewage  was  $13.12  per  million  gallons.  The  degree  to  which 
organic  matter  was  removed,  as  measured  by  albuminoid  am- 
monia, was  89.1  per  cent  for  the  first  method  and  89.2  per  cent 
for  the  second.  The  process  of  nitrification  was,  however,  more 


198  DISPOSAL   OF   SEWAGE.  V. 

complete  in  the  first  method,  the  amount  of  nitrogen  as  nitrates 
being  4.86  parts  per  million  as  against  1.96  for  the  second. 

The  operation  of  sewage  filter  beds  in  winter  is  not  found  to 
be  attended  with  difficulty,  for  the  temperature  of  the  sewage 
is  higher  than  that  of  the  air.  At  Brockton,  Mass.,  the  lowest 
temperature  of  the  sewage  as  it  reached  the  beds  has  been  found 
to  be  about  40°  F.  in  March,  while  the  highest  is  about  64°  in 
September.  When  the  flow  of  sewage  is  discontinued  in  winter, 
freezing  of  the  surface  sometimes  occurs,  and  it  was  found  at 
Brockton  that  furrowed  beds  are  preferable  to  flat  ones,  since  the 
sewage  then  more  easily  melts  the  frost  and  penetrates  into  the 
sand.  In  summer  vegetables  are  sometimes  grown  upon  the 
beds  and  then  the  flow  of  sewage  is  regulated  to  the  needs 
of  the  crops,  this  flow  being  usually  smaller  than  when  filtration 
is  alone  the  object  in  view. 

68.   BROAD  IRRIGATION. 

Irrigation  by  water  has  been  practiced  from  the  earliest  times 
in  countries  where  the  annual  rainfall  is  less  than  20  inches, 
the  rainfall  of  the  wet  months  being  stored  in  reservoirs  from 
which  it  is  distributed  to  the  fields  in  the  dry  months  by  means 
of  canals  and  ditches.  The  disposal  of  the  sewage  of  towns  by 
means  of  irrigation  is,  on  the  other  hand,  a  modem  method  which 
was  originated  in  England  about  1870,  and  in  which  the  principles 
of  common  irrigation  are  combined  with  those  of  intermittent 
filtration.  It  should  be  said,  however,  that  the  disposal  of  liquid 
kitchen  wastes  by  running  them  into  gardens  has  always  been 
practiced  by  farmers,  and  indeed  the  universal  custom  of  spread- 
ing the  contents  of  privies  and  cesspools  upon  the  fields  is  an 
imperfect  application  of  the  method  on  a  small  scale. 

When  a  system  of  beds  is  prepared  for  the  disposal  of  sewage 
by  intermittent  filtration,  vegetables  may  be  planted  upon  some 
of  the  beds  in  the  spring  and  only  a  small  quantity  of  sewage 
be  applied  to  them  during  the  summer,  the  main  work  of  puri- 


68.  BROAD    IRRIGATION.  1 99 

fi cation  being  confined  to  the  other  beds.  The  beds  which  are 
planted  are  not  those  which  have  been  especially  prepared  in 
layers  of  gravel  and  sand,  but  are  areas  on  which  the  natural 
soil  has  been  left  undisturbed  except  in  the  places  where  trenches 
have  been  dug  for  the  underdrains.  The  sewage  is  brought 
along  the  side  of  one  of  these  beds  in  a  ditch,  from  which  it  flows 
in  lateral  ditches  or  furrows  between  the  rows  of  growing  vege- 
tables and  is  absorbed  by  the  soil.  The  quantity  of  sewage  thus 
furnished  must  be  so  regulated  that  the  ground  may  not  become 
wet  enough  to  interfere  with  the  normal  healthy  growth  of  the 
vegetables;  this  quantity  can  be  determined  only  by  experience, 
as  it  depends  upon  the  kind  of  soil  and  growing  plants  and  upon 
the  amount  of  rainfall.  The  effect  of  the  application  of  sewage 
is  like  that  of  manure;  the  organic  matter  is  decomposed  in  the 
soil  under  the  action  of  bacteria  and  the  resulting  products  are 
absorbed  by  the  roots  of  plants  as  materials  for  their  growth. 

Broad  irrigation,  or  sewage  farming,  as  it  is  often  called,  is 
the  application  of  sewage  upon  fields  not  only  for  the  purpose 
of  disposing  of  it,  but  to  utilize  it  as  manure  for  the  growing 
crops.  The  area  needed  to  thus  dispose  of  the  sewage  of  a 
town  is  much  larger  than  that  required  in  the  method  of  inter- 
mittent filtration,  in  fact  from  10  to  20  times  as  large,  but  the 
expense  of  underdraining  and  embankments  is  much  smaller 
per  acre,  and  it  is  expected  that  a  good  profit  will  be  derived 
from  the  sale  of  the  crops. 

The  best  location  for  a  sewage  farm  is  where  the  surface  has 
a  fair  slope  toward  a  stream  and  where  the  soil  is  dry  and 
porous.  A  part  of  the  area  should  be  laid  out  in  specially  per- 
pared  beds  to  be  operated  by  the  method  of  intermittent  filtration 
when  the  sewage  is  not  needed  on  the  fields,  but  over  the  greater 
part  the  soil  is  left  undisturbed  except  where  underdrains  are 
needed.  The  number  of  these  drains  will  depend  upon  the 
character  of  the  soil  and  the  slope  of  the  surface ;  moist  and  level 
ground  must  be  well  underdrained,  but  dry  and  sandy  soil  with 


200  DISPOSAL    OF    SEWAGE.  V. 

a  sloping  surface  needs  few  if  any  drains.  Sometimes  open 
ditches  may  serve  as  drains,  but  more  commonly  tiles  are  laid 
about  five  feet  deep,  the  direction  of  the  lines  of  tiles  running 
normal  to  the  contour  curves  of  the  surface,  so  that  their  grades 
may  be  as  great  as  possible. 

The  sewage  is  carried  to  the  fields,  if  possible,  by  gravity, 
the  main  sewer  from  the  town  being  extended  nearly  to  the  farm, 
where  it  changes  into  an  open  masonry  conduit,  in  which  a  screen 
is  placed  to  intercept  the  rags  and  coarse  material.  From  this 
conduit  the  sewage  passes  through  gates  into  ditches  which  lead 
to  different  parts  of  the  farm,  and  from  these  ditches  lateral  furrows 
convey  it  between  the  rows  of  vegetables.  All  of  these  channels 
are  laid  out  with  respect  to  the  contours  of  the  surface,  so  that 
the  flow  may  be  neither  too  fast  nor  too  slow,  and  many  gates 
are  provided  for  shutting  off  and  regulating  the  discharge.  These 
details,  in  fact,  are  practically  the  same  as  those  which  have 
been  so  long  used  in  irrigating  fields  by  water. 

The  application  of  sewage  to  the  different  fields  must  be  inter- 
mittent, and  often  several  days  may  elapse  between  the  intervals 
of  watering.  While  one  part  of  the  farm  is  watered,  another 
part  is  being  planted,  cultivated,  or  harvested,  or  is  at  rest. 
During  periods  of  rainfall,  or  in  the  winter,  when  the  fields  need 
no  sewage,  it  is  turned  upon  the  beds  of  the  intermittent-filtration 
area.  To  secure  success  in  the  purification  of  the  sewage  and  at 
the  same  time  produce  good  crops,  constant  and  intelligent 
supervision  of  the  processes  of  watering  and  resting  is  indispen- 
sable. The  crops  which  are  raised  on  sewage  farms  are  not 
limited  to  vegetables,  but  wheat,  oats,  and  grasses  have  been 
grown  with  success;  in  some  cases  three  or  four  crops  of  grass 
have  been  obtained  in  one  year  where  only  one  crop  could  be 
produced  on  unirrigated  soil. 

The  operation  of  filtration  areas  in  winter  has  not  been  found 
so  difficult  as  might  be  expected.  As  the  temperature  of  the 
sewage  is  higher  than  that  of  the  air  and  soil,  the  ground  is 


68.  BROAD    IRRIGATION.  2OI 

generally  prevented  from  freezing,  and  hence  the  process  of 
purification  goes  on,  although  the  rate  of  nitration  must  be  lower 
than  in  the  summer,  since  the  activity  of  the  bacteria  is  not  as 
great.  In  some  cases  special  ditches  have  been  made  to  receive 
the  sewage  in  winter  instead  of  spreading  it  over  the  surface, 
its  absorption  into  the  beds  being  through  the  bottom  and  sides 
of  these  ditches.  In  a  severe  climate,  where  the  temperature 
may  be  below  20  degrees  Fahrenheit  for  several  weeks,  more  or 
less  trouble  will  be  experienced  from  freezing. 

In  Europe  the  system  of  broad  irrigation  for  the  disposal  of 
sewage  is  extensively  used  and  has  been  found  to  be  a  satisfactory 
one;  the  health  of  the  farmers  is  good,  the  sewage  of  the  circles 
is  effectively  turned  into  harmless  and  useful  constituents,  and 
the  crops  sometimes  yield  a  fair  profit. 

Sewage  farming  is  most  advantageous  in  arid  regions  where 
irrigation  by  water  is  necessary  in  order  to  grow  crops  on  good 
land;  here  poor  soil  irrigated  by  sewage  may  produce  good  crops. 

In  ^899  Rafter  described  143  plants  in  the  United  States  and 
Canada  which  disposed  of  sewage  by  the  method  of  broad  irrigation 
or  that  of  intermittent  filtration,  or  by  a  combination  of  both.  The 
system  of  broad  irrigation  was  first  tried  at  Pullman,  111.,  in  1887, 
but  the  level  groundrand  dense  soil  was  not  such  as  to  insure  success 
and  the  plant  was  abandoned  after  a  few  years.  A  large  plant  of 
this  type  at  Los  Angeles,  CaL,  was  abandoned  in  1905  after  opera- 
ting for  some  years.  Other  plants  have  also  been  abandoned  in 
recent  years  and  but  few  such  plants  are  now  constructed.  Objec- 
tions to  the  system  have  been  based  on  odors,  on  the  transmission 
of  disease  by  insects,  and  to  the  use  of  vegetables  grown  on  such 
farms,  especially  such  vegetables  which  are  eaten  in  a  raw  state. 
In  general  it  may  be  said  that  the  method  of  sewage  disposal  by 
broad  irrigation  in  this  country  is  not  successful  and  it  is  very 
improbable  that  it  will  be  adopted  to  any  extent  in  the  future. 

The  largest  sewage  farms  are  those  at  Paris  and  Berlin,  the 
former  city  having  13  100  acres  and  the  latter  17  500  acres  under 


202  DISPOSAL    OF    SEWAGE.  V. 

irrigation  in  1903.  Paris  disposed  of  12  300  gallons  per  acre 
per  day  at  a  cost  of  $11  per  million  gallons,  while  Berlin  disposed 
of  3530  gallons  per  acre  per  day  at  a  cost  of  $9  per  million  gallons. 
At  Paris  the  land  is  rented  to  farmers  at  $30  per  acre  per  year, 
but  at  Berlin  the  farms  are  operated  by  the  city.  At  Berlin  there 
was  a  profit  in  thirteen  of  the  eighteen  years  following  1885,  and 
the  net  profit  in  1903  was  $95  ooo. 

69.    SEPTIC  TANKS. 

A  septic  tank  is  a  basin  or  reservoir  in  which  sewage  is  stored 
until  it  reaches  the  septic  stage  of  decomposition  (Art.  62).  In 
this  stage  the  anaerobic  bacteria  are  actively  at  work  changing  the 
sewage  into  gas  which  rises  to  the  surface,  while  the  heavier 
organic  and  the  inorganic  matter  form  a  sludge  at  the  bottom. 
The  effluent  from  the  tank  is  much  purer  than  the  sewage  and 
may  be  discharged  into  a  stream  with  less  danger,  or  may  more 
easily  be  further  treated  by  intermittent  filtration.  On  the  sur- 
face of  the  stored  sewage  a  scum  forms  during  this  process  which 
acts  to  exclude  the  air  and  thus  permit  the  multiplication  of  the 
anaerobic  bacteria.  The  sewage  is  introduced  below  this  scum, 
flows  slowly  through  the  tank  at  the  proper  rate,  and  the  effluent 
is  usually  discharged  in  such  a  manner  that  it  may  be  aerated 
so  as  to  destroy  offensive  odors. 

A  common  cesspool  with  open  bottom,  such  as  may  be  found 
in  many  American  villages,  is  an  example  of  a  septic  tank  on  a 
small  scale.  The  sewage  and  drainage  of  a  house  sometimes 
flows  into  such  a  cesspool  for  many  years  without  the  deposit 
of  sludge  becoming  of  sufficient  depth  to  cause  the  liquid  to 
overflow  at  the  top.  With  a  perfect  adjustment  of  bacterial 
action  to  the  quantity  and  quality  of  the  sewage,  there  might 
perhaps  be  no  deposit  of  sludge  at  the  bottom  except  that  due 
to  inorganic  matter,  all  the  organic  matter  being  converted  into 
gas  and  the  liquid  effluent. 

The  degree  of  purification  by  means  of  a  septic  tank  depends 


69.  SEPTIC   TANKS.  203 

upon  the  rate  of  flow  as  well  as  upon  the  character  of  the  sewage. 
In  practice  the  rate  of  flow  through  the  tank  is  often  too  rapid 
to  permit  full  septic  action,  so  that  different  analyses  of  the 
sewage  and  effluent  give  variable  results.  When  a  tank  holds 
twenty-four  hours'  flow  of  sewage,  a  reduction  of  about  one- 
half  of  the  total  solids  is  generally  found,  as  also  a  reduction 
of  from  30  to  60  per  cent  in  organic  matter  as  measured  by  oxy- 
gen consumed  or  albuminoid  ammonia.  There  is,  however,  a 
marked  increase  in  free  ammonia,  as  also  in  the  dissolved  organic 
matter.  On  the  whole,  the  degree  of  removal  of  organic  matter 
is  about  the  same  as  that  secured  by  the  process  of  chemical 
precipitation;  the  number  of  bacteria  removed  is,  however,  far 
less  in  the  septic  method,  and  in  some  cases  the  bacteria  are 
more  abundant  in  the  effluent  than  in  the  sewage. 

The  credit  for  the  introduction  of  the  septic  tank  is  frequently 
given  to  Cameron,  who  in  1894  took  out  a  patent  in  England; 
but  patents  covering  the  same  idea  had  been  taken  in  1881  by 
Mouras  in  France,  in  1881  by  Glover  in  the  United  States,  and 
in  1891  by  Moncrieff  in  England.  The  first  installation  of  the 
system  was  made  by  Cameron  at  Exeter,  England,  in  1896, 
where  a  tightly  covered  tank,  18X68  feet  in  size  and  9  feet  deep, 
received  about  50  coo  gallons  of  sewage  per  day.  The  sewage 
first  entered  a  grit  chamber,  from  which  it  passed  to  the  tank, 
flowing  through  it  in  twenty-four  hours,  and  the  effluent  after 
aeration  was  filtered  upon  beds  of  coke  having  a  total  area  of 
3600  square  feet.  Through  a  pipe  at  the  top  of  the  tank  the  gas 
escaped  and  was  burned  for  illuminating  purposes.  In  1899 
the  operation  of  the  tank  had  reached  a.  state  of  permanency,  and 
there  was  a  scum  2  inches  in  thickness  on  the  top  and  a  deposit 
of  sludge  36  inches  deep  at  the  bottom;  around  the  tanks  and 
beds  there  was  no  offensive  odor.  In  1901  the  accumulation  of 
sludge  had  become  so  great  that  it  was  necessary  to  remove 
a -portion  of  it.  In  1902  there  was  completed  at  Exeter  a  larger 
plant  of  six  septic  tanks  designed  to  treat  3  ooo  coo  gallons  of 
sewage  per  day. 


204  DISPOSAL   OF    SEWAGE.  V. 

Since  1896  numerous  septic  tanks  have  been  installed  in  Europe 
and  America  for  the  purpose  of  treating  sewage  before  turning 
in  upon  filter  beds.  In  1897,  Talbot  built  a  septic  tank  at  Cham- 
paign, III,  having  a  capacity  of  22  200  gallons,  for  the  treatment 
of  a  sewage  flow  ranging  from  250000  to  600000  gallons  per 
day,  and  this  gave  very  satisfactory  results  as  to  purification, 
notwithstanding  the  high  rate  of  flow.  In  1898  small  installations 
were  made  at  Ames,  la.,  and  Verona,  N.  J.,  and  a  little  later  the 
septic  tank  became  widely  recognized  in  America  as  one  of  the 
most  valuable  methods  for  the  treatment  of  sewage  preliminary 
to  filtration.  The  experience  in  England  tends  toward  the  con- 
clusion that  open  tanks  work  nearly  as  well  as  closed  ones,  the  sur- 
face scum  being  sufficient  to  exclude  the  air  after  it  has  once 
formed.  In  order  to  avoid  disturbing  this  scum,  it  is  desirable  that 
provision  should  be  made  to  draw  off  the  sludge,  when  neces- 
sary, by  a  siphon  or  by  drains. 

While  the  term  septic  tank  implies  that  the  sewage  has  reached 
the  septic  state  in  which  the  aerobic  bacteria  have  disappeared 
and  the  anaerobic  bacteria  are  actively  at  work,  the  sizes  of  the 
tanks  and  the  consequent  rates  of  flow  usually  employed  are 
such  as  to  render  it  probable  that  the  decomposition  of  the  sewage 
has  often  not  progressed  much  further  than  the  stale  stage. 
Bacterial  analyses  shoeing  the  number  of  bacteria  in  the  effluent 
to  be  greater  than  in  the  sewage  are  not  uncommon,  and  this 
tends  to  confirm  the  above  conclusion.  For  instance,  experiments 
were  made  by  Johnson  at  Columbus,  O.,  in  1905,  with,  two  tanks 
40  feet  long,  8  feet  wide,  and  about  7  feet  deep;  through  the 
first  of  these  1 7  ooo  gallons  of  sewage  were  passed  in  sixteen  hours, 
and  through  the  second  the  same  amount  was  passed  in  twenty- 
four  hours.  The  average  number  of  bacteria  in  the  sewage 
during  the  six  months,  January-June,  was  i  250  ooo  per  cubic 
centimeter,  while  the  average  number  In  the  effluent  from  the 
first  tank  was  3  600  ooo  and  that  in  the  effluent  from  the  second 
tank  was  4  250  ooo  per  cubic  centimeter. 


69.  SEPTIC    TANKS.  205 

When  a  septic  tank  is  put  into  service,  its  operation  should  be 
so  conducted  that  the  septic  action  may  be  developed  as  soon 
as  possible.  The  first  indication  of  this  action  is  gas  arising 
from  the  surface,  and  this  is  not  generally  observed  until  after 
two  or  three  weeks;  the  surface  scum,  however,  is  not  usually 
fairly  formed  until  after  three  or  four  months  of  use;  in  the 
Columbus  experiments  above  mentioned  there  was  no  well- 
defined  scum  formation  after  eight  months  of  service.  It  is 
generally  considered  that  satisfactory  septic  action  is  not  estab- 
lished until  this  scum  has  formed  to  exclude  the  air.  It  hence 
appears  to  follow  that  the  rate  of  flow  during  the  first  one  or 
two  months  of  use  should  be  slow  enough  to  permit  the  septic 
state  to  become  fully  developed;  perhaps  later  the  flow  can  be 
materially  accelerated  and  the  septic  action  still  be  maintained, 
especially  in  the  bottom  of  the  tank.  The  degree  of  purification 
required  will  depend  upon  the  disposal  of  the  effluent.  When 
the  effluent  is  turned  into  a  stream,  it  is  desirable  that  it  should 
not  produce  foul  odors  and  that  the  purification  should  rapidly 
continue  in  the  water  of  the  stream;  in  such  cases  it  is  probably 
best  that  the  sewage  should  not  reach  the  complete  septic  state, 
but  that  the  bacteria  in  the  effluent  should  be  mostly  aerobic,  so 
that  they  may  continue  the  process  of  inoffensive  decomposition. 
Whatever  be  the  disposition  of  the  effluent,  its  condition  should 
be  non-putrescible,  namely,  such  that  no  subsequent  putrefaction 
may  be  liable  to  occur. 

The  septic  tanks  described  in  this  article  are  the  so-called 
"  single-story  tanks."  The  latest  development  in  septic  tanks  is  the 
two-story  tank,  and  of  several  forms  of  these  the  Imhoff  Tank 
is  now  most  in  favor.  This  tank  will  be  described  in  the  follow- 
ing article. 

69a.  IMHOFF  TANKS. 

Since  1906  the  single-story  septic  tank  has  not  proven  as  satis- 
factory as  had  been  expected  due  to  the  presence  of  masses  of 
sludge,  broken  up  by  the  ebullition  of  gas,  in  the  effluent.  Con- 


2050 


DISPOSAL  OF  SEWAGE. 


V. 


siderable  dissatisfaction  has  also  been  caused  on  account  of  the 
patent  claims  covering  this  type  of  tank,  and  from  the  litigation 
arising  therefrom. 

The  first  two-story  tanks  are  the  invention  of  Travis,  who  built 
and  patented  such  a  tank  at  Hampton,  England,  in  1903,  In 
this  tank,  however,  while  most  of  the  sewage  flowed  through  the 


-.  tfOas  vent 


VERTICAL  SECTION  OF  IMHOFF  TANK. 

upper  compartment,  a  portion  of  it  also  flowed  through  the  lower 
compartment  or  digestion  chamber. 

The  Imhoff  or  Emscher  tank  was  devised  by  Karl  Imhoff  in 
the  Emscher  District  in  Germany  in  1906.  It  is  essentially  tfye 
same  as  the  Travis  tank  except  that  there  is  no  flow  of  the  sewage 
in  the  digestion  chamber.  The  sewage  flows  through  the  upper, 
or  sedimentation  chamber,  which  acts  in  exactly  the  same  manner 
as  a  plain  sedimentation  tank,  and  the  sludge  is  retained  in  the 
lower  compartment,  where  it  is  digested  or  rotted  by  the  action 
of  the  anaerobic  bacteria. 

The  figure  shows  the  general  arrangement  of  an  Imhoff  tank. 
The  sludge  is  pumped  out,  or  drawn  off  by  gravity,  if  the  topo- 
graphical conditions  admit,  at  varying  intervals  depending  on 
the  sewage,  and  is  disposed  of  in  the  same  manner  as  the  sludge 


yo.  CONTACT  BEDS.  2056 

from  the  single-story  tanks  described  in  the  last  article.  Imhofif 
tanks  are  usually  built  in  Germany  of  the  radial  flow  type,  in  which 
the  tank  is  circular,  the  sewage  entering  the  tank  at  the  center  and 
being  discharged  at  the  circumference.  In  America  the  horizontal 
flow  type  seems  to  be  preferred.  In  this  the  sedimentation 
chambers  are  rectangular,  the  sewage  entering  at  one  end  and 
discharging  at  the  other,  and  the  digestion  chambers  are  either 
circular  or  rectangular,  the  latter  being  more  popular  with  American 
engineers.  The  period  of  retention  in  this  tank  is  much  less  than 
for  the  single-story  tank,  ranging  from  one  to  three  hours,  depend- 
ing on  the  strength  of  the  sewage. 

All  surfaces  in  the  sedimentation  chamber  should  be  made  as 
smooth  as  practicable  to  prevent  particles  of  matter  from  adhering 
to  them  and  they  should  be  frequently  scraped  or  washed.  Unless 
the  sewage  is  well  screened,  scum  boards  should  be  provided  to 
prevent  floating  matter  from  reaching  the  effluent. 

The  main  difference  between  the  Imhoff  tank  and  the  Travis  tank 
lies  in  the  overhanging  lip  on  the  slots  connecting  the  upper  and 
lower  chambers.  This  overhang  prevents  gases  and  broken  up 
sludge  from  rising  and  mingling  with  the  fresh  sewage  passing 
through  in  the  sedimentation  chambers  above. 

The  sludge,  after  removal  from  the  tanks,  is  dried  on  a  sludge 
bed  consisting  of  10  or  12  inches  of  gravel,  broken  stone  or  cinders 
covered  with  a  thin  layer  of  sand  and  underlaid  with  drains.  The 
sludge  is  spread  over  this  to  a  depth  of  about  i  foot  and  will,  under 
ordinary  conditions,  be  sufficiently  dried  in  ten  or  twelve  days  to 
be  removed.  It  is  practically  odorless  and  makes  a  very  good 
fertilizer. 

70.  CONTACT  BEDS. 

The  principles  of  the  intermittent  nitration  of  sewage,  ex- 
plained in  Art.  67,  have  been  applied  in  the  system  known  as 
that  of  contact  beds,  whereby  it  is  aimed  to  secure  more  perfect 
bacterial  action  and  a  higher  degree  of  purification.  A  contact 


206  DISPOSAL  OF  SEWAGE.  V- 

bed  is  generally  arranged  with  sides  and  bottom,  so  built  that 
no  leakage  occurs  when  it  is  rilled,  and  the  sewage  is  allowed  to 
remain  quiescent  in  the  bed  for  several  hours  before  the  effluent 
is  drained  off  through  the  exit  valves.  In  this  process  of  drain- 
ing air  flows  into  the  voids  of  the  filtering  material  which  were 
formerly  occupied  by  the  sewage,  and  after  a  period  of  rest  the 
bed  is  again  filled.  The  filtering  material  is  generally  of  uniform 
size  throughout  the  bed,  and  it  is  the  intention  that  the  bacterial 
action  shall  take  place  throughout  the  entire  depth. 

In  the  process  of  intermittent  filtration,  the  sewage  is  applied 
on  the  surface  where  it  stands  to  a  certain  depth  and  is  forced 
through  the  bed  by  gravity,  leaving  a  deposit  on  the  surface 
which  must  be  removed  at  certain  intervals;  as  in  water  filtration, 
the  greater  part  of  the  bacterial  action  takes  place  in  the  upper 
layer  of  the  bed.  In  the  contact  bed,  however,  the  sewage  may 
be  introduced  below  the  surface  through  pipes,  or,  when  it  is 
introduced  at  the  top,  there  is  no  flow  through  the  exit  valves, 
and  only  sufficient  sewage  is  introduced  to  completely  fill  the 
voids  in  the  filtering  material.  A  contact  bed  is  always  much 
smaller  than  a  filter  bed,  so  that  the  periods  of  filling,  standing, 
draining,  and  rest  may  be  subject  to  better  regulation.  While 
these  periods  vary  considerably  in  length,  depending  upon  the 
size  of  the  bed  and  the  character  of  the  sewage,  a  total  time  of 
about  four  hours  has  been  often  used  for  the  four  operations,  the 
filling  occupying  about  half  an  hour,  the  sewage  standing  quiescent 
in  the  bed  about  two  and  a  half  hours,  the  draining  occupying  half 
an  hour,  and  the  period  of  rest  another  half  hour.  Occasionally 
longer  periods  of  rest  are  allowed,  these  generally  being  in  the 
night. 

The  theory  of  the  action  of  these  beds  may  be  explained  by 
starting  with  the  period  of  rest  when  the  voids  in  the  filtering 
material  are  filled  with  air.  Sewage  being  then  slowly  introduced, 
the  aerobic  bacteria  obtain  a  bountiful  supply  of  air  and  the 
filtering  material  furnishes  a  great  amount  of  surface  of  contact 
for  the  liquid.  Along  this  surface  of  contact  between  liquid 


70.  CONTACT    BEDS.  207 

and  filtering  material,  it  is  believed  that  the  bacteria  work  rapidly 
and  effectively,  while  the  sewage  is  quiet  during  the  period  of 
standing.  The  period  of  draining  then  allows  air  to  flow  in, 
and  the  period  of  rest  enables' the  aeration  to  extend  effectively 
throughout  the  entire  bed.  The  action  of  the  contact  bed  is 
hence  entirely  bacterial,  this  being  promoted  by  the  supply  of 
oxygen,  and  the  standing  period  should  not  be  longer  than  is 
required  for  the  bacteria  to  completely  utilize  this  oxygen. 

Contact  beds  were  first  used  in  England  in  1893  and  1895, 
the  credit  of  their  development  being  due  to  Dibdin,  and  many 
have  been  there  constructed  since  1900.  The  area  of  each  bed 
is  on  the  average  about  one- tenth  of  an  acre.  The  filtering 
material  often  employed  has  been  stone  or  slag,  broken  to  a 
tolerably  uniform  size,  say  from  J  to  f  inch  in  size,  although 
finer  material  like  sand  or  burnt  clay  has  been  used  and  advocated. 
Porosity  of  the  material  was  regarded  as  of  much  importance 
prior  to  1900,  and  a  patented  article  called  polarite,  made  by 
blowing  air  through  hot  furnace  slag,  was  advocated  as  affording 
a  large  extent  of  contact  surface.  The  depth  of  the  beds  is  usually 
from  4  to  6  feet.  Before  applying  the  sewage  to  the  beds,  it  is 
well  screened,  and  often  a  preliminary  treatment  by  sedimentation, 
or  by  septic  tanks  is  employed,  so  as  to  reduce  the  amount  of 
suspended  organic  matter. 

Few  contact  beds  have  been  built  in  the  United  States.  At 
Depew,  N.  Y.,  four  coke  beds  were  constructed  in  1901  to  filter 
the  effluent  of  a  septic  tank;  the  period  of  operation  was  seven 
hours,  the  bed  being  filled  in  140  minutes,  the  sewage  standing 
in  it  for  eighty  minutes,  and  the  time  of  emptying  and  aeration 
being  200  minutes.  At  Marion,  O.,  four  broken-stone  beds 
were  built  in  1905,  to  filter  the  effluent  of  septic  tanks,  the  period 
of  operation  being  ten  hours;  the  effluent  from  these  contact 
beds  passes  through  sand  filters  and  the  final  effluent  is  said  to 
be  clear,  colorless,  and  odorless. 

The  purification  effected  by  a  contact  bed  consists  in  the  re- 


208  DISPOSAL  OF  SEWAGE.  V. 

duction  of  the  dissolved  organic  matter,  and  the  amount  of 
this  reduction,  according  to  the  experiments  made  at  Manchester, 
England  in  1899,  is  about  50  per  cent.  By  having  beds  in  series, 
so  that  the  second  bed  receives  the  effluent  of  the  first,  and  the 
third  that  of  the  second,  it  was  claimed  that  each  bed  effects' a 
reduction  of  50  per  cent  of  the  organic  matter  of  the  liquid  that 
it  receives,  so  that  the  effluent  from  the  third  bed  has  been  purified 
to  the  extent  of  about  87  per  cent.  This  conclusion,  however, 
has  not  been  generally  accepted,  and  experiments  made  at  Leeds, 
England,  in  1902,  showed  that  a  single  contact  bed  effected  a 
reduction  in  organic  matter  of  72  per  cent  as  measured  by  albu- 
minoid ammonia  and  87  per  cent  as  measured  by  oxygen  con- 
sumed. Experiments  at  Columbus,  O..  in  1905,  on  contact  beds 
'both  of  broken  stone  and  of  crushed  coke  gave  reductions  of 
60  per  cent  for  the  stone  and  58  per  cent  for  the  coke  as  measured 
by  oxygen  consumed,  while  the  percentages  were  85  and  82  as 
measured  by  the  volatile  organic  matter,  and  the  reduction  in 
bacteria  was  60  and  45  per  cent  respectively. 

Sometimes  there  occurs  a  clogging  of  the  voids  in  the  filtering 
material  which  diminishes  the  efficiency,  so  that  a  renewal  of  the 
material  may  be  necessary.  Fine  and  porous  materials  seem  more 
liable  to  become  clogged  than  coarser  ones,  and  Dibdin  constructed 
in  1904  a  primary  contact  bed  in  which  layers  of  broken  slate  were 
used,  these  layers  being  2  inches  apart  and  supported  by  slate 
blocks.  This  slate  filling  occupied  only  18  per  cent  of  the  volume 
of  the  bed,  but  after  fourteen  months'  use  some  clogging  had 
occurred  which  was  readily  removed  by  flushing.  The  purifica- 
tion effected  by  this  slate  contact  bed  was  found  to  be  about  52  per 
cent,  a  larger  figure  than  those  obtained  from  other  beds  in  which 
limestone,  brick,  slag,  and  clinker  were  used  as  filtering  ma- 
terials. 

While  contact  beds  have  given  very  good  results  in  smaller 
installations  they  do  not  seem  to  be  as  economical  for  larger  plants 
as  sprinkling  filters. 


71.  SPRINKLING  FILTERS.  2OQ 

71,    SPRINKLING  FILTERS. 

All  the  methods  thus  far  described  for  the  filtration  of  sewage 
have  been  intermittent,  that  is,  the  flow  of  sewage  upon  the  bed 
is  discontinued  at  times  in  order  that  the  bed  may  be  drained 
to  permit  the  entrance  of  air  into  it.  This  drainage  and  aeration 
occupies  time,  and  if  this  time  can  be  saved  by  making  the  flow 
continuous,  without  reducing  the  degree  of  purification,  economy 
Vvill,be  promoted.  Much  attention  has  hence  been  given  to 
the  subject  of  securing  a  continuous  flow  of  the  effluent  through 
the  filter  bed  and  at  the  same  time  furnishing  to  the  inflowing 
sewage  an  ample  supply  of  air. 

The  term  sprinkling  filter  refers  to  a  filter  bed  in  which  the 
sewage  is  applied  to  the  surface  in  the  form  of  a  spray  whereby 
air  is  thoroughly  mingled  with  it.  The  terms  trickling  filter 
and  dribbling  filter  are  also  sometimes  used  with  the  same  signifi- 
cation. The  development  of  these  filters  began  in  England  about 
the  same  time  as  that  of  contact  beds,  and  the  economy  derived 
by  their  use  has  been  so  marked  that  many  installations  of  the 
system  have  been  made. 

In  the  United  States  the  adoption  of  sprinkling  filters  has  been 
less  rapid,  but  since  1908  quite  a  number  of  installations  have  been 
put  into  service  and  their  use  has  been  proposed  for  many  other 
places.  Among  the  plants  constructed  may  be  mentioned  those  at 
Columbus,  O.,  10  acres;  Baltimore,  Md.,  14  acres;  and  smaller 
areas  at  Mount  Vernon,  N.  Y.,  Washington,  Pa.,"Waterbury,  Conn., 
Atlanta,  Ga.,  Batavia,  N.  Y.,  and  a  number  of  smaller  places. 
Experiments  in  this  direction  were  conducted  by  the  Massachusetts 
State  Board  of  Health  as  early  as  1889. 

The  material  used  in  these  filters  is  generally  broken  stone  of  a 
size  ranging  from  i  to  2.5  inches,  the  bed  being  from  5  to  8  feet 
deep,  and  resting  upon  a  sub-bed  of  larger  stones  which  surround 
the  lateral  and  main  drains.  The  sewage,  which  is  usually  pre- 
viously screened  and  a  portion  of  the  solids  removed  by  sedi- 
mentation, is  brought  through  pipes,  placed  sometimes  just  below 


20ga  DISPOSAL  OF  SEWAGE.  V. 

/ 

the  surface  of  the  bed  and  sometimes  in  a  gallery  between  beds, 
and  distributed  onto  the  beds  through  nozzles.  These  are  usually 
fixed  and  give  circular  or  square  sprays.  Care  should  be  taken 
to  have  them  so  spaced  that  they  cover  the  entire  filter  bed.  This 
spacing  is  usually  from  12  to  14  feet  depending  on  the  head  on  the 
nozzle,  which  is  generally  made  from  5  to  8  feet.  Trouble  is  some- 
times experienced  from  nozzle  clogging,  but  in  the  latest  types  this 
is  not  apt  to  be  serious.  The  surface  of  the  bed  sometimes  becomes 
clogged  with  the  coarse  particles  in  the  sewage,  or  with  vegetable 
growths  and  worms.  These  may  be  removed  by  raking,  but  a  more 
inexpensive  method  seems  to  be  to  apply  hypochlorite  of  lime.  The 
sewage  is  often  held  in  sedimentation  tanks  for  a  period  of  from 
two  to  four  hours,  after  filtering,  to  remove  a  portion  of  the  solids 
which  are  practically  as  great  in  the  effluent  as  in  the  influent. 

The  rate  of  flow  of  the  sewage  through  continuous  sprinkling 
filters  is  usually  much  higher  than  that  through  common  inter- 
mittent filter  beds,  and  the  degree  of  purification  is  very  much 
lower.  Experiments  made  at  Columbus,  O.,  in  1905,  indicate, 
however,  that  sprinkling  filters  are  superior  to  contact  beds  in 
regard  to  the  non-putrescibility  of  the  effluent,  even  when  the 
rate  of  flow  for  the  former  is  double  that  of  the  latter. 

In  the  Columbus  experiments  satisfactory  results  were  secured 
from  continuous  sprinkling  filters  with  a  rate  of  2  ooo  ooo  gallons 
per  acre  per  day,  the  effluent,  however,  being  very  impure  compared 
with  that  obtained  by  the  method  of  intermittent  filtration  described 
in  Art.  67.  The  following  averages  of  the  analyses  made  for  one 
of  the  sprinkling  filters  af  Columbus  give  a  more  definite  idea 
of  the  degree  of  purification : 

Influent.  Effluent. 

Total  solids,                       parts  per  million  921  850 

Organic  (volatile),      "      "       "  168  118 

Inorganic,  753  732 

Free  Ammonia,                     "      "       "  10.7  6.8 

Nitrogen  as  nitrates              "      "       "  2.6 

Oxygen  consumed  43  26 

Bacteria,  per  cubic  centimeter  2  500  ooo  750  ooo 


710.  OTHER   METHODS    OF   SEWAGE   PURIFICATION.  2096 

These  figures,  compared  with  those  in  Art.  67,  show  a  very 
imperfect  purification,  yet  it  was  sufficient  to  render  the  effluent 
non-putrescible  and  permit  it  to  be  safely  discharged  into  a 
stream  after  a  period  of  sedimentation.  The  percentage  of 
reduction  in  bacteria  is  here  70  per  cent,  but  some  analyses  for 
coli  bacteria  showed  300  ooo  and  35  ooo  per  cubic  centimeter 
for  influent  and  effluent  respectively,  which  indicate  a  reduction 
of  88  per  cent. 

The  recent  development  and  operation  of  the  sprinkling  filter 
have  proved  its  success  as  an  agent  in  purifying  sewage  to  the  extent 
of  production  a  practically  stable,  non-putrescible  effluent  which 
may  be  safely  discharged  into  most  streams  without  further 
treatment,  unless  it  be  some  additional  sedimentation.  These 
filters  will  operate  continuously  at  as  high  a  rate  as  2  oco  oco 
gallons  per  acre  per  day  or  higher,  and  if  no  material  finer  than 
i  inch  be  used  in  the  beds  there  is  little  danger  of  serious  clogging. 
As  a  general  proposition  it  may  be  stated  that  the  deeper  the 
bed  and  the  lower  the  rate  of  application  of  the  sewage  to  the  bed, 
the  greater  will  be  the  degree  of  purification.  The  cost  for  opera- 
tion and  maintenance  of  the  Columbus  plant  for  the  year  1910, 
from  the  report  of  Mr.  Jackson,  Engineer  in  Charge,  was  $2.14 
per  million  gallons  of  sewage  treated. 

710.    OTHER  METHODS  OF  SEWAGE  PURIFICATION. 

In  addition  to  the  various  methods  of  sewage  purification  dis- 
cussed in  the  foregoing  articles,  brief  mention  may  be  made  of 
several  other  processes  which  have  received  more  or  less  attention 
bysengineers  and  scientists. 

Aeration,  as  the  name  implies,  has  for  its  aim  the  purification 
of  sewage  by  oxidizing  the  organic  matter  contained  therein  by  the 
oxygen  present  in  the  air.  It  has  been  found  a  difficult  matter 
to  replenish  the  dissolved  oxygen  in  the  sewage  as  fast  as  it  is  con- 
sumed by  the  action  of  the  aerobic  bacteria.  If  this  could  be 
accomplished  the  purifying  of  sewage  could  be  completed  by  the 


2IO  SEWAGE   DISPOSAL.  V. 

action  of  the  aerobic  bacteria  entirely  and  the  putrefaction  with 
its  disagreeable  odors  and  other  bad  features  caused  by  the  action 
of  the  anaerobic  bacteria  would  not  become  a  part  of  the  process 
of  purifying  sewage.  Thus  far  this  process  has  hardly  advanced 
beyond  the  laboratory  stage. 

The  use  of  electricity  in  purifying  sewage,  as  well  as  water,  has 
received  considerable  attention  from  time  to  time  and  while  it 
has  as  yet  developed  only  as  far  as  the  experimental  stage,  several 
plants  have  been  constructed  which  employ  the  electrolytic  method, 
as  it  is  called.  The  process  is  due  to  experiments  by  Webster 
made  at  a  number  of  places  in  England  in  1889.  When  an  electric 
current  is  passed  through  water  the  water,  as  well  as  the  dis- 
solved chlorides  of  sodium,  calcium,  magnesium,  etc.,  are  broken 
up  into  their  several  parts  and  new  salts  are  formed  and  oxygen, 
hydrogen,  and  chlorine  are  liberated  as  gases.  The  action  of  some 
of  the  salts  is  to  form  precipitates  which  drag  down  the  suspended 
matter  in  the  water  or  sewage  and  the  oxygen  acts  to  oxidize  the 
organic  matter  present.  The  chlorine  often  combines  to  form 
the  hypochlorites  of  sodium  and  calcium,  which  with  itself  are 
strong  disinfectants.  Experiments  have  shown  that  the  use  of 
iron  or  aluminum  plates  used  for  the  electrodes  give  the  best  results, 
the  former  being  preferable  on  account  of  its  lesser  cost.  The 
oxygen  and  chlorine  liberated  at  the  positive  pole  attack  the  iron 
plate  and  oxide  of  iron  is  formed,  which  is  precipitated.  The 
negative  pole  is  not  attacked  and  in  order  that  the  iron  electrodes 
may  wear  evenly  the  current  is  reversed  from  time  to  time.  Plants 
have  been  installed  at  Santa  Monica,  a  suburb  of  Los  Angeles, 
Cal.,  and  at  Oklahoma  City  for  the  treatment  of  sewage  by  the 
electrolytic  method.  It  is  stated  that  the  percentage  of  reduc- 
tion of  organic  matter  is  about  50  per  cent  at  Santa  Monica.  At 
Oklahoma  City  the  reduction  in  bacteria  is  said  to  be  from  98 
to  99  per  cent  according  to  Fuller  in  his  book  entitled  Sewage 
Disposal  (New  York,  1911).  No  other  information  is  available 
as  to  the  character  of  the  effluent  so  that  comparisons  as  to  the  rela- 


72.  COMPARISON  OF  METHODS.  211 

tive  efficiency  and  economy  of  this  method  with  the  other  methods 
commonly  in  use,  cannot  be  made. 

Sterilization  of  sewage  by  the  addition  of  a  disinfectant  has 
received  considerable  attention  in  the  past  and  has  lately  been 
revived  since  the  introduction  of  hypochlorite  of  lime  in  sterilizing 
water  supplies.  There  is  no  doubt  that  the  addition  of  an  amount 
of  hypochlorite  of  lime  to  sewage  will  decrease  the  number  of  bacteria 
very  materially,  often  as  high  as  from  95  to  99  per  cent  being 
removed.  This  will,  of  course,  prevent  the  action  of  the  anerobic 
bacteria  and  consequent  putrefaction.  The  main  objection  seems 
to  be  that,  even  with  this  degree  of  sterilization,  when  the  effluent 
is  discharged  into  a  water-course  the  bacteria  there  present  begin 
work  on  the  organic  matter  in  the  sewage  and  putrefaction  and  its 
attendant  nuisances  may  occur  at  some  distance  down  the  stream. 
It  has  the  advantage,  however,  of  probably  destroying  all,  or 
practically  all,  of  the  pathogenic  bacteria.  When  hypochlorite 
is  used  it  should  be  applied  to  settled  sewage  rather  than  to  crude 
sewage,  as  the  latter  contains  larger  particles  of  solids  which  are 
disinfected  only  on  the  surface  and  the  bacteria  in  them  are  not 
destroyed.  The  sterilization  process  has  been  used  to  some  extent 
in  this  country,  especially  to  prevent  the  pollution  of  oyster  beds. 

72.   COMPARISON  OF  METHODS. 

The  various  systems  and  methods  for  the  disposal  of  sewage 
have  now  been  briefly  described  and  discussed.  The  simplest 
and  oldest  of  these,  which  can  scarcely  be  called  a  method,  is  to 
discharge  the  sewage  into  a  river  or  into  the  ocean,  giving  no 
thought  as  to  the  subsequent  pollution  that  may  occur.  Such 
is  the  method  still  in  use  at  New  York  and  at  the  large  cities  near 
it  in  New  Jersey,  the  consequence  being  that  the  water  flowing 
out  of  the  harbor  often  causes  offense  to  neighboring  towns  along 
the  coast.  The  problem  here  arising  is  a  difficult  one,  the  solution 
of  which  is  not  easily  seen,  but  the  time  is  not  far  distant  when  it 
must  be  seriously  attacked. 


212  DISPOSAL   OF    SEWAGE.  V. 

The  method  of  chemical  precipitation  effects  such  a  degree  of 
purification  that  the  effluent  may  often  be  discharged  into  a 
stream  without  producing  ill  results  when  the  water  of  the  stream 
is  not  to  be  used  for  a  public  supply.  This  method,  on  account 
of  its  expense,  has  been  gradually  going  out  of  use  in  the  United 
States  since  1895. 

The  method  of  the  intermittent  filtration  of  raw  sewage  through 
sand  beds  and  the  method  of  broad  irrigation  require  large  areas 
of  land  which  it  is  often  impossible  to  obtain  near  large  cities. 
Under  favorable  conditions,  however,  these  methods  effect  a 
higher  degree  of  purification  than  can  be  secured  by  any  other 
system,  while  a  fair  return  is  sometimes  obtained  from  crops 
grown  upon  the  surface.  The  process  of  purification  is  here 
bacterial  in  close  imitation  with  that  of  nature,  the  slowness  of 
the  action  enabling  the  aerobic  bacteria  to  complete  the  work  of 
nitrification  so  that  the  effluent  is  practically  pure  water. 

The  septic  tank,  the  contact  bed,  and  the  sprinkling  filter 
generally  effect  a  degree  of  purification  no  greater  than  that 
obtained  in  chemical  precipitation.  The  effluent  from  these 
plants  is  still  foul,  but  the  purification  has  extended  so  far  that 
it  may  often  be  safely  discharged  into  a  stream.  These  methods  are 
often  combined  with  each  other,  the  effluent  from  a  septic  tank 
passing  through  a  contact  bed  or  through  a  sprinkling  filter;  or, 
to  secure  a  still  higher  degree  of  purification,  slow  sand  beds  or 
irrigation  fields  may  be  added. 

For  example,  the  plant  completed  about  1915  at  Baltimore, 
Md.,  consists  of  sedimentation  tanks,  rotary  screens,  sprinkling 
filters,  and  final  settling  tanks,  in  the  order  named.  Sterilization 
of  the  effluent  with  hypochlorite  has  also  been  considered  if  found 
necessary  to  protect  the  shellfish  in  Chesapeake  Bay.  Imhoff 
tanks  have  recently  been  added  for  the  preliminary  treatment. 

It  is  seen  from  this  brief  discussion  that  the  complete  and 
satisfactory  purification  of  sewage  can  only  be  obtained  by  the 
methods  of  slow  sand  filtration  and  broad  irrigation.  Such 


72.  COMPARISON   OF  METHODS.      [|  213 

complete  purification  is  not  always  needed,  nor  can  the  money  be 
kept  in  view.  Only  an  expert  can  have  a  full  understanding 
of  the  field  of  sewage  disposal  and  utilization,  and  only  an  expert 
can  make  designs  for  a  plant  which  shall  be  both  efficient  and 
economical.  Even  the  expert  cannot  make  these  designs  without 
much  study  of  existing  plants,  and  experiments  are  often  necessary 
to  arrive  at  decisive  conclusions. 

As  an  illustration  of  the  work  sometimes  necessary  in  design, 
it  may  be  noted  that  at  Columbus,  O.,  studies  occupying  nearly 
seven  years  were  made  by  Griggs,  Alvord,  Hering,  and  others,  and 
$46  ooo  was  spent  during  1904  and  1905  in  a  thorough  series  of 
experiments  on  chemical  precipitation,  plain  sedimentation, 
septic  tanks,  sand  beds,  contact  beds,  and  sprinkling  filters. 
The  details  of  these  experiments  and  the  final  conclusions  were 
published  in  1905  in  a  volume  of  499  pages,  this  being  a  report 
by  Johnson,  the  engineer  in  charge  of  the  testing  station.  The 
plan  recommended  a  process  consisting  of  three  parts;  first, 
a  preliminary  septic  treatment  in  basins  holding  about  an  eight- 
hour  flow;  second,  purification  of  the  septic  effluent  to  a  non- 
putrescible  state  by  sprinkling  filters  at  an  average  rate  of  2  ooo  ooo 
gallons  per  acre  per  day;  third,  clarification  of  the  effluent  from 
the  filters  in  basins  holding  an  average  flow  of  about  two  hours. 
This  process  produces  a  final  effluent  of  satisfactory  appearance 
from  which  about  90  per  cent  of  the  bacteria  in  the  raw  sewage 
has  been  removed.  Work  on  the  construction  of  a  plant  for  the 
city  in  accordance  with  these  plans  was  begun  in  1906  and  com- 
pleted in  1908,  the  cost  of  the  entire  work  being  $i  350  ooo. 

In  the  year  1893  only  31  cities  and  towns  in  the  United  States 
had  systems  of  sewage  purification;  in  1902  there  were  95  cities 
and  towns  of  3000  population,  and  upwards,  which  had  such 
systems.  In  1902  there  were  27  plants  which  used  intermittent 
filtration,  21  which  used  broad  irrigation,  22  which  used  septic 
tanks,  and  10  which  used  chemical  precipitation.  In  1915  there 


214  DISPOSAL  OF  SEWAGE.  V. 

were  several  hundred  plants  in  operation  and  the  list  is  constantly 
growing.  The  methods  of  broad  irrigation  and  chemical  precipi- 
tation are  now  seldom  employed  and  sprinkling  filters  are  dis- 
placing contact  beds.  Intermittent  sand  nitration  is  only  used 
where  beds  of  suitable  material  are  available  close  at  hand  and  the 
single-story  septic  tank  has  given  way,  to  a  large  extent,  to  the 
two-story  tank.  The  rapid  growth  of  sewage  disposal  works 
has  resulted  from  the  realization  by  the  public  that  the  health  of 
the  community  is  promoted  by  preventing  the  pollution  of  streams 
and  other  sources  of  water  supply. 

73.  EXERCISES  AND  PROBLEMS. 

62.  Consult  Reports  of  the  Massachusetts  State  Board  of  Health, 
and  ascertain  further  facts  regarding  the  decomposition  and  purification 
of  sewage. 

63  (a)  Consult  Engineering  News,  Feb.  19,  1903,  and  ascertain 
the  conclusions  of  the  English  commission  regarding  the  presence  of 
Bacillus  coli  communis  as  an  index  of  river  pollution. 

63  (&)  Consult  Sedgwick's  article  in  Report  of  State  Board  of  Health 
of  Massachusetts  for  1892,  and  give  details  regarding  the  transmission  of 
typhoid-fever  germs  in  the  Merrimac  River  from  Lowell  to  Newburyport. 

64.  Describe  the  method  of  screening  sewage  through  hay  and  sand 
which  was  used  at  Atlantic  City,  N.  J.,  in  1893. 

65  (a)  Describe  the  combined  screening,  aeration,  and  nitration  plant 
constructed  at  Reading,  Pa.,  in  1897. 

65  (b)  Consult  Fuller's  Sewage  Disposal  (New  York,  1912)  and  obtain 
facts  regarding  the  Weand  Segregator  at  Reading,  Pa. 

66  (a)  If  100  pounds  of  lime  are  added  to  water  containing  sufficient 
carbon  dioxide  to  completely  react  with  it,  how  many  pounds  of  calcium 
carbonate  will  be  precipitated? 

66  (6)  Consult  Rafter  and  Baker's  Sewage  Disposal  in  the  United 
States  (New  York,  1895),  and  describe  the  chemical  precipitation  tanks 
at  Worcester,  Mass,  with  the  method  of  operating  them. 

67  (a)  Describe  the  intermittent-filtration  beds  at  Brockton,   Mass, 
or  those  at  Pittsfield,  Mass. 

67  (&)  Consult  Annual  Report  of  the  Massachusetts  State  Board  of 
Health  for  1903  and  find  results  obtained  at  various  intermittent  sand 
filtration  plants  in  Massachusetts. 


73-  EXAMPLES  AND  PROBLEMS.  215 

68.  Consult  Rafter's  Sewage  Irrigation  (U.  S.  Geological  Survey, 
Washington,  1897)  and  describe  the  sewage  farms  at  Berlin  and  Paris. 

69  (0)  Read  Hering's  article  on  Bacterial  Processes  of  Sewage  Puri- 
fication in  Engineering  Magazine,  Sept.,  1898,  and  give  an  account  of 
the  process  of  septic  decomposition. 

69  (b)  Describe  the  septic  tanks  at  Plainfield,  N.  J.,  and  those  at 
Pawtucket,  R.  I. 

69  (<;)  Consult  Engineering  News,  1901,  1902,  and  1906,  and  obtain 
information  regarding  various  patents  for  the  septic  tank  and  lawsuits 
for  alleged  infringement. 

69  (</)  Consult  Fuller's  Sewage  Disposal  (New  York,  1912),  and  deter- 
mine the  proper  size  for  the  digestion  chamber  of  an  Imhoff  tank.  Also 
the  proper  size  for  a  sludge-drying  bed. 

70.  Consult  Johnson's  Report  on  Sewage  Purification  at  Columbus, 
O.  (1905),  and  give  further  facts  in  regard  to  the  history  of  the  develop- 
ment of  contact  beds. 

71  (a)  Consult  recent  reports  of  the  Massachusetts  State  Board  of 
Health  and  make  notes  of  their  findings  from  experiments  with  sprinkling 
filters. 

71  (6)  Consult  paper  by  Gregory  in  the  Transactions  of  the  American 
Society  of  Civil  Engineers  for  June,  1910,  and  obtain  sketches  of  the  sprink- 
ling filters  at  Columbus. 

72  (a)  Consult    Engineering   Record,    August    n,    1906,    and   obtain 
facts  regarding  the  sewage  of  Paterson,  N.  J.,  with  an  outline  of  the 
plan  proposed  by  Hazen  for  its  purification. 

72  (&)  Obtain  details  of  the  sewage  disposal  plant  at  Baltimore,  Md. 

73  (a)  Ascertain   the   conclusions   published   in   April,    1907,   regard- 
ing eight  years'  work  on  trickling  filters  by  the  Massachusetts  State 
Board  of  Health. 

73  (£>)  Mention  five  processes  of  sewage  treatment  tested  at  New  Haven 
Conn,  in  1917;  see  Engineering  News-Record,  Nov.  i,  1917. 

73  (c)  Consult  Engineering  News-Record,  Nov.  15,  1917,  and  describe 
methods  used  for  sewage  disposal  at  army  cantonments  in  the  United 
States. 


2T6  REFUSE   AND   GARBAGE.  VI. 


CHAPTER  VI. 
REFUSE  AND  GARBAGE. 
74.    PRIVIES  AND  CESSPOOLS. 

In  the  country  districts  and  in  many  villages  the  waste  water 
from  the  houses  is  thrown  upon  or  conducted  to  the  garden, 
while  the  animal  excrements  in  the  barn-yards  and  the  human 
excrements  in  the  privies  are  annually  spread  upon  the  fields. 
In  many  towns  of  considerable  size,  the  method  for  the  disposal 
of  house  water  and  human  excrement  is  by  cesspools.  A  privy 
and  a  cesspool  are  essentially  the  same  in  principle,  both  being 
holes  or  vaults  in  the  ground,  but  the  former  is  shallow  and  open 
at  the  top,  while  the  latter  is  deeper  and  has  its  top  covered. 
The  common  country  privy  is  usually  an  offensive  place,  but  a 
cesspool  may  be  arranged  so  as  to  be  cleanly  in  comparison. 
The  privy  receives  only  human  excrements,  but  the  cesspool 
usually  receives  both  these  and  the  kitchen  drainage  and  often 
also  some  of  the  roof  water. 

Wherever  the  population  is  dense  the  privy  system-  is  sure  to 
produce  disease,  especially  when  the  drinking  water  is  obtained 
from  neighboring  wells.  Even  when  the  drinking  water  is  not 
contaminated  by  the  privy,  flies  may  carry  the  bacteria  of  disease 
from  the  privy  to  the  kitchen.  It  is  a  well-established  fact  that 
the  epidemics  of  typhoid  fever  which  prevailed  at  military  camps 
in  the  United  States  and  West  Indies  during  the  Spanish  War  of 
1898  were  largely  due  to  flies,  which  carried  the  germs  of  the 
disease  from  the  privy  deposits  to  the  food  of  the  soldiers. 


74-  PRIVIES    AND    CESSPOOLS.  217 

The  hole  which  forms  the  privy  or  cesspool  is  walled  up  with 
stone,  and  a  common  practice  in  the  country  is  to  have  the  walls 
of  loose  stone,  so  that  the  liquid  material  may  leak  through  them 
into  the  surrounding  soil.  The  result  of  this  is  a  gradually  in- 
creasing pollution  of  the  soil,  and  often  a  neighboring  spring  or 
well  becomes  contaminated  so  as  to  cause  disease.  For  instance, 
near  Easton,  Pa.,  in  August,  1898,  twelve  cases  of  typhoid  fever 
and  two  deaths  resulted  from  the  use  of  spring  water  which  had 
become  infected  from  a  cesspool;  the  spring  had  previously  been 
condemned  by  the  board  of  health,  but,  in  spite  of  the  warning, 
the  people  of  the  neighborhood  continued  to  drink  its  water. 
Thousands  of  such  cases  are  given  in  medical  journals  and  in 
reports  of  boards  of  health. 

In  a  well-regulated  village  the  privy  and  cesspool  vaults  are 
required  to  be  built  with  tight  walls  and  bottoms,  so  that  no 
leakage  into  the  soil  may  occur,  and  their  contents  are  to  be 
removed  at  regular  intervals  under  the  supervision  of  the  board 
of  health.  This  operation  should  be  done  by  a  contractor  who 
has  the  special  apparatus  for  effecting  the  removal  with  the 
least  nuisance  and  who  is  required  to  use  disinfectants  upon 
the  material,  the  vault,  and  the  apparatus  in  order  to  destroy 
the  odors,  kill  the  bacteria,  and  thus  prevent  contamination  of 
the  air. 

Earth,  charcoal,  ashes,  and  similar  substances  are  deodorizers, 
but  not  disinfectants.  A  substance  is  said  to  be  a.  disinfectant 
when  it  acts  upon  decaying  matter  so  as  to  stop  the  process  of 
decay,  and  this  is  done  by  its  poisonous  action  upon  the  bacteria. 
When  the  bacteria  are  deprived  of  life  the  decomposition  ceases 
and  the  gases  which  accompany  decay  or  putrefaction  are  no 
longer  evolved.  Carbolic  acid,  iron  sulphate,  chloride  of  lime, 
sodium  hypochlorite,  and  many  other  chemicals  are  efficient 
disinfectants,  and  their  proper  application  in  the  cleaning  of  a 
privy  or  cesspool  will  prevent  all  offense  and  render  the  operation 
harmless.  The  men  who  do  such  cleaning  cannot,  however, 


2l8  REFUSE  AND  GARBAGE.  VI. 

be  trusted  to  effect  thorough  disinfection,  and  it  is  hence  important 
that  an  inspector  of  the  board  of  health  should  always  be  present 
to  strictly  enforce  the  regulations. 

The  pneumatic  cart  is  the  best  apparatus  for  cleaning  a  privy 
or  cesspool  vault.  This  has  an  air-tight  cylinder  mounted  on 
wheels  and  in  general  appearance  resembles  a  watering  cart. 
The  material  in  the  vault  should  be  in  a  semi-liquid  state,  which 
can  be  effected  by  the  addition  of  water,  if  necessary.  A  hose 
leads  from  the  cylinder  to  the  vault,  and  the  valve  in  the  hose 
is  closed  until  the  air  has  been  exhausted  from  the  cylinder  by 
means  of  an  air  pump;  the  valve  is  then  opened  and  the  atmos- 
pheric pressure  forces  the  liquid  up  into  the  cylinder.  This 
process  is  repeated  until  the  cart  is  filled  or  the  vault  entirely 
emptied.  Almost  the  only  danger  in  this  operation  is  the  con- 
tamination of  the  atmosphere  by  the  air  pumped  out  of  the 
cylinder.  When  the  pump  is  driven  by  a  portable  steam  engine, 
the  exhausted  air  may  be  pumped  through  the  fire  under  the 
boiler;  when  the  pump  is  driven  by  hand,  the  exhausted  air 
may  be  carried  into  a  barrel  of  water  containing  carbolic  acid  or 
Some  other  powerful  disinfectant  in  solution. 

The  disposal  of  the  material  is  a  difficult  part  of  the  problem. 
In  Europe,  where  manure  is  valuable,  it  may  often  be  sold  to 
the  peasants;  in  America  farmers  will  allow  it  to  be  spread  on 
their  fields,  but  will  rarely  pay  for  it.  In  any  event  the  method 
of  disposal  as  manure  is  restricted  to  the  country,  and  a  town 
which  uses  the  cesspool  method  is  forced  to  dump  the  material 
into  streams  or  to  bury  it  in  the  ground.  The  nuisance,  vexa- 
tion, and  expense  of  the  cesspool  method  become  in  time  so  great 
that  the  town  abandons  it  and  substitutes  a  water-carriage  system 
of  sewage  removal. 

The  privy  and  cesspool  methods  must  long  continue  to  be 
used  in  the  country  and  in  villages,  but  the  fact  that  diphtheria 
and  typhoid  fever  are  more  common  in  the  country  than  in  the 
city  should  serve  as  a  continual  warning.  An  ounce  of  prevention 


75-  HOUSE   AND    STREET    REFUSE.  21 9 

is  worth  more  than  a  pound  of  cure  in  all  sanitary  matters.  The 
daily  use  of  dry  earth  in  country  privies,  municipal  regulations 
for  tight  vaults  and  proper  removal  in  villages,  the  organization  of 
an  efficient  board  of  health  in  towns  and  frequent  sanitary  in- 
spections by  it,  are  preventives  which  are  too  often  regarded 
as  unnecessary  because  the  health  of  the  community  appears 
to  be  fair. 

75.   HOUSE  AND  STREET  REFUSE. 

The  waste  matter  of  houses,  besides  that  discharged  through 
the  drains,  is  of  three  kinds:  the  first  consists  of  animal  and 
vegetable  matter  from  the  kitchen,  which  is  called  garbage; 
the  second  consists  of  dust  and  ashes;  and  the  third,  known  as 
rubbish,  consists  of  broken  crockery,  tin  cans,  rags,  paper,  old 
metals,  and  worn-out  household  articles.  In  the  village  the 
disposal  of  these  is  left  to  the  householder;  he  utilizes  the  garbage 
as  food  for  animals,  he  throws  the  ashes  upon  the  fields,  or  uses 
it  to  build  walks,  he  burns  the  combustible  part  of  the  rubbish 
and  disposes  of  the  remainder  as  best  he  can.  After  the  village 
becomes  a  town,  the  garbage  is  often  carried  away  by  farmers, 
and  when  this  proves  unprofitable  a  public  scavenger  is  appointed 
to  collect  it  and  cart  it  into  the  country  to  be  dumped  upon  waste 
fields.  When  the  town  grows  into  a  city,  all  three  classes  of 
refuse  are  collected  and  removed. 

The  separation  of  the  refuse  into  these  three  classes  should  be 
insisted  upon  in  all  systems  of  public  removal,  or,  at  least,  the 
garbage  should  never  be  placed  in  vessels  containing  ashes  and 
rubbish.  In  the  town  each  householder  disposes  of  his  ashes 
and  rubbish,  while  the  municipality  removes  the  garbage.  In 
the  city  both  are  to  be  removed  by  the  municipality,  but  in  separate 
vessels.  The  mineral  matter  and  some  of  the  vegetable  matter 
of  the  rubbish  often  has  a  market  value  sufficient  to  pay  for 
cartage,  while  the  ashes  may  be  used  to  fill  low  lands.  The 
bones  in  the  garbage  are  worth  a  little,  but  the  greater  part 
has  generally  no  value,  and  one  of  the  most  effective  methods 


220  REFUSE   AND    GARBAGE.  VI* 

for  its  disposal  is  to  burn  it  in  a  garbage  crematory.  The  rubbish 
is  sorted  into  salable  and  worthless  articles,  and  much  of  the 
latter  kind  is  also  burned  in  refuse  incineratories.  In  large  citie? 
a  considerable  sum  is  derived  from  the  sale  of  articles  sorted  out 
from  the  rubbish.  For  example,  the  following  is  a  list  of  a  few 
of  the  salable  materials  at  one  of  the  yards  in  New  York  during 
1899,  this  yard  collecting  the  refuse  of  116  ooo  people:  905  301 
pounds  of  newspapers,  461  385  pounds  of  manila  paper,  587  208 
pounds  of  strawboard,  18  620  pounds  of  books,  41  450  pounds 
of  white  rags,  200495  pounds  of  black  rags,  21  070  pounds  of 
twine,  about  90000  pounds  of  carpet,  38  160  pounds  of  shoes, 
80800  pounds  of  wire,  2090  pounds  of  zinc,  1607  pounds  of 
brass,  nearly  10  ooo  pounds  of  rubber,  as  also  numerous  tin  cans 
bottles,  brooms,  hats,  and  other  articles. 

Another  kind  of  refuse  is  that  of  dead  animals.  In  the  country 
these  are  buried  in  the  ground,  but  in  the  cities  the  smaller  animals 
are  collected  with  the  garbage,  while  the  large  ones  are  carted 
to  the  cremation  or  reduction  plants.  The  product  of  the  privies 
and  cesspools,  which  is  usually  called  night  soil,  forms  a  distinct 
class  by  itself  which  is  to  be  removed  in  special  closed  carts  as 
explained  in  Art.  74. 

The  cost  of  the  removal  and  disposal  of  these  house  wastes 
is  a  considerable  item  in  the  budget  of  a  municipality.  For 
example,  Washington,  D.  C.,  paid  in  1906  for  the  removal  and 
disposition  of  ashes,  $54  ooo,  for  garbage  and  dead  animals 
$80  761,  for  night  soil  $16  500,  and  for  rubbish  $16  500,  making 
a  total  of  $167  761,  or  about  40  cents  per  person  per  year. 

The  street  refuse  consists  of  the  droppings  of  animals,  paper, 
dust,  and  of  many  of  the  articles  enumerated  above  under  the  head 
of  rubbish.  This  refuse  is  collected  by  daily  sweepings  and 
removed  by  carts;  its  character,  after  the  rubbish  is  sorted  out, 
is  so  largely  organic  that  it  may  readily  be  burned,  and  this  is 
a  common  method  for  its  disposal  in  large  cities.  In  some  cities 
the  ashes  and  street  sweepings  are  removed  together,  this  being 


75-  STREET    CLEANING.  221 

especially  the  case  where  they  are  to  be  loaded  on  scows  and 
dumped  at  sea. 

For  Philadelphia,  Pa.,  the  average  amount  of  house  and  street 
refuse  per  capita  per  day  removed  and  disposed  of  during  the 
year  1903  was  as  follows:  1.19  pounds  of  garbage,  1.68  pounds 
of  ashes,  0.06  pound  of  rubbish,  and  0.37  pound  of  street  sweep- 
ings, making  a  total  of  3.30  pounds.  Similar  figures  for  the 
Borough  of  Manhattan  in  the  City  of  New  York  for  the  same 
year  are:  0.53  pounds  of  garbage,  0.34  pounds  of  rubbish,  and 
4.02  pounds  of  ashes  and  street  sweepings,  making  a  total  of 
4,89  pounds  per  capita  per  day. 

The  methods  for  the  disposal  of  this  house  and  street  refuse 
reach  the  highest  perfection  in  the  large  cities.  Garbage  is 
either  burned  in  incinerators  (Art.  78)  or  treated  in  reduction 
plants  (Art.  79).  Ashes  are  utilized  to  fill  up  low  lands,  as 
also  are  the  worthless  metallic  materials  of  the  rubbish.  The 
worthless  combustible  part  of  the  rubbish  is  burned,  and  the 
street  sweepings  are  either  burned  or  dumped  at  sea. 

76.    STREET  CLEANING. 

The  refuse  that  accumulates  in  the  streets  consists  mainly  of 
manure,  paper,  leaves,  and  soil  which  has  been  ground  into 
dust.  The  amount  of  dust  depends  upon  the  character  of  the 
street  pavements  and  may  be  ten  times  as  great  on  a  macadam 
as  on  an  asphalt  pavement,  while  the  amount  of  the  other  matters 
depends  upon  the  character  of  the  business  and  traffic.  As  a 
rough  average  about  1000  cubic  yards  of  refuse  per  year  accumu- 
lates on  each  mile  of  pavement  in  a  densely  populated  city  and 
the  removal  of  this  costs  about  $500  per  year. 

Each  owner  of  property  along  a  street  is  expected  to  sweep 
and  wash  his  sidewalk;  in  towns  where  gutters  are  laid  between 
the  sidewalk  and  street  the  property  owner  is  also  generally 
expected  to  build  and  clean  them.  Generally  this  refuse  is 
merely  swept  upon  the  street  pavement  proper,  from  which 


222  REFUSE    AND    GARBAGE.  VI. 

it  is  afterwards  removed  by  the  municipal  authorities.  Under 
the  best  regulations  the  property  owner  has  nothing  to  do  with 
the  construction  or  maintenance  of  gutters,  and  indeed  there 
should  be  no  gutters  other  than  those  formed  by  the  slight  trans- 
verse slope  of  the  pavement  to  the  curbs. 

The  character  of  a  street  pavement  influences  to  a  certain 
degree  the  health  of  the  adjacent  neighborhood.  The  old  cob- 
blestone pavement,  retaining  foul  animal  matter  between  and 
under  the  stones,  was  a  continual  menace  to  health.  The  early 
wooden  pavement  was  clean  when  new,  but  after  a  few  years 
of  use  it  began  to  rot  and  to  absorb  the  liquid  animal  wastes, 
so  that  the  dust  arising  from  it  was  filled  with  bacteria.  The 
macadam  pavement,  though  excellent  in  suburban  localities, 
wears  quickly  into  mud  and  dust  under  the  traffic  of  a  city  street. 
The  brick  pavement  and  the  granite-block  pavement,  when  laid 
with  close  joints  on  a  concrete  foundation,  produce  little  dust 
and  can  be  kept  in  a  fairly  cleanly  condition.  An  asphalt  pave- 
ment is  in  all  respects  the  best  on  hygienic  grounds,  as  it  absorbs 
no  filth  and  can  be  cleaned  with  less  expense  than  any  other 
kind.  Asphalt  pavements  and  creosoted  -wooden  blocks  have 
been  laid  on  Broadway  in  New  York  since  1900,  replacing  the 
former  granite-block  pavement. 

In  villages  the  streets  are  left  to  be  cleaned  by  the  storm  water, 
and  their  surfaces  are  renewed  by  annual  repairs.  When  the 
village  becomes  a  town  and  builds  macadam  pavements,  an- 
nual or  semi-annual  scrapings  are  instituted  to  remove  the  dust. 
When  the  town  becomes  a  city  and  the  macadam  pavement  is 
replaced  by  brick  or  asphalt,  sweeping  and  cleaning  must  be 
done  weekly  or  oftener,  and  when  the  city  is  a  large  one  with 
heavy  traffic  in  its  streets  these  operations  are  generally  carried 
on  every  day. 

Scraping  may  be  done  on  a  brick  or  asphalt  pavement,  or  on  a 
tolerably  smooth  stone  surface;  when  cleaning  is  done  by  scrapers 
it  should  be  preceded  by  sprinkling,  so  that  the  dirt  may  be 


76.  STREET  CLEANING.  223 

more  easily  removed.  Scraping  is  most  commonly  used  when 
the  accumulation  of  material  is  large,  as  may  be  the  case  with 
a  weekly  cleaning.  The  scraping  is  done  by  machines  drawn 
by  men  or  horses,  the  work  being  begun  along  the  middle  of  the 
street,  and  the  material  gradually  moved  toward  the  sides,  where 
it  is  made  into  piles  ready  for  loading  into  carts. 

Sweeping  is  a  better  method  than  scraping  when  the  work 
is  carried  on  daily.  Rotary  sweepers  having  a  series  of  brooms 
on  a  revolving  axle  are  extensively  used;  when  in  motion  the 
axle  is  inclined  toward  the  side  of  the  street  so  as  to  carry  the 
refuse  in  that  direction.  Hand  sweeping  is  also  widely  done 
to  supplement  the  work  of  the  machines,  especially  upon  stone 
pavements.  One  man  can  clean  from  500  to  1000  square  yards 
of  surface  per  hour,  but  a  machine  operated  by  a  man  and  a 
horse  will  sweep  an  area  ten  times  as  great. 

The  work  of  street  cleaning  begins  in  the  evening  and  con- 
tinues through  the  night,  the  carting  being  done  after  midnight. 
In  some  European  cities  the  sweeping  is  followed  by  washing; 
hydrant  streams  are  turned  on  and  men  with  brooms  thoroughly 
wash  the  asphalt  pavements.  The  streets  in  European  cities 
are  as  a  rule  far  cleaner  than  those  in  America,  but  excellent 
results  have  been  secured  in  New  York  through  the  system 
introduced  by  Waring  about  1895,  and  the  reform  has  since  been 
extended  to  other  cities.  The  streets  of  European  villages  are, 
however,  rarely  in  as  good  sanitary  condition  as  those  of  Amer- 
ican villages. 

The  disposal  of  street  refuse  is  often  effected  by  carting  it 
into  the  suburbs,  where  it  can  be  deposited  to  fill  up  swamps 
or  low  lands.  In  large  cities  on  the  seacoast  it  is  sometimes 
loaded  upon  scows  which  dump  it  into  the  ocean.  When  the 
street  surfaces  are  free  from  dust,  the  sweepings  are  almost 
entirely  animal  and  vegetable  matter,  so  that  they  may  be  com- 
bined with  the  house  garbage  and  be  burned  or  digested  in  gar- 
bage furnaces.  In  some  European  localities  farmers  will  remove 


224  REFUSE    AND    GARBAGE.  VI. 

this  matter  for  use  as  fertilizer,  but  in  America  it  rarely  has 
sufficient  value  to  pay.  for  cartage.  In  cities  which  have  the 
combined  system  of  sewerage,  some  of  the  street  sweepings 
have  been  dumped  into  the  catch  basins  during  times  of  storms, 
but  this  is  not  a  good  practice,  and  should  not  be  allowed  except 
under  the  strict  supervision  of  the  engineer  in  charge  of  the 
sewers. 

The  problem  of  economical  street  cleaning  is  one  of  effective 
organization  of  men  and  methods,  and  hence  comes  under  the 
province  of  the  engineer.  That  it  has  not  been  done  well  and 
economically  in  American  cities  is  mainly  due  to  the  circumstance 
that  its  direction  has  been  intrusted  to  councilmen  and  their 
political  adherents,  instead  of  putting  it  under  the  charge  of 
the  city  engineer.  The  work  of  the  engineer,  like  that  of  the 
army  and  navy,  has  nothing  to  do  with  any  political  party,  but 
is  conducted  for  the  welfare  of  the  community  only.  To  secure 
the  highest  efficiency  and  economy  in  street  cleaning  and  other 
public  engineering  works,  the  same  methods  must  be  adopted 
as  those  used  by  a  private  corporation,  namely,  to  select  the 
best  men,  let  out  the  work  to  contract  when  advisable,  and  by 
vigilant  superintendence  and  inspection  secure  the  required  results 
with  the  least  expense. 

77.    GARBAGE  REMOVAL  AND  DECAY. 

An  imperfect  method  of  garbage  removal,  often  used  in  towns, 
is  to  require  each  householder  to  provide  his  own  vessel,  the  contents 
of  which  are  dumped  into  an  open  wagon  in  its  weekly  rounds.  This 
is  objectionable  because  the  dirty  vessel  is  not  always  cleaned  by 
the  servants,  and  because  the  garbage  on  the  wagon  causes  more  or 
less  unpleasantness  in  the  streets.  The  ideal  method  is  to  have  the 
municipality  furnish  and  clean  the  vessels;  starting  on  his  round 
with  a  wagon  load  of  clean  empty  vessels,  the  scavenger  leaves 
one  at  each  house  and  takes  a  full  one  in  its  place.  These 


77^  GARBAGE   REMOVAL  AND  DECAY.  2  25 

vessels  should  have  covers  which  can  be  fastened  with  a  hasp, 
and  thus  the  transportation  through  the  streets  causes  no  offense. 
The  size  of  the  vessels  is  such  that  they  may  be  filled  during  the 
interval  between  two  collections,  and  under  the  best  regulations 
this  interval  is  not  longer  than  two  days. 

When  garbage  is  dumped  upon  scows  to  be  carried  out  to  sea,  it 
is  sometimes  sprinkled  with  lime  in  order  to  neutralize  the  odors 
of  decay.  In  this  method  of  disposal  the  ashes  and  street  sweep- 
ings may  be  combined  with  the  garbage.  The  method  of  dis- 
posal at  sea  is  a  satisfactory  one  if  the  scows  go  several  miles 
away  from  land,  but  otherwise  the  garbage  may  be  washed  back 
upon  shore  by  the  currents  and  storms.  The  method  of  spread- 
ing the  garbage  upon  fields  is  rarely  an  efficient  one,  unless  it  be 
carried  far  into  the  country  and  only  a  small  amount  applied  in 
one  place.  To  render  either  method  fully  satisfactory  a  large 
expense  for  transportation  results. 

The  theory  of  the  purification  of  garbage  by  dumping  it  into 
water  or  by  spreading  it  on  land  is  the  same  as  that  given  in  the 
first  chapter  to  account  for  the  transformation  of  dead  into  living 
organic  matter.  In  both  cases  oxygen  (O)  is  furnished  to  attack 
the  carbon  (C),  and  thus  carbon  dioxide  (CO2)  is  evolved.  Next 
nitrogen  (N)  and  hydrogen  (H)  are  liberated,  these  combining 
to  form  ammonia  (NH3),  which  upon  further  oxidation  becomes 
nitrous  acid  (HNO2)  and  nitric  acid  (HNOs);  these  acids  by 
combination  with  metallic  compounds  produce  nitrites  (MNO2) 
and  nitrates  (MNOs).  Also  the  hydrogen  combines  with  oxygen 
to  form  water  (H2O).  Thus  under  the  favorable  condition  of 
the  presence  of  abundant  oxygen,  the  dead  organic  matter  becomes 
resolved  into  harmless  gases  and  solids.  But  if  sufficient  oxygen 
be  not  furnished,  the  process  of  decomposition  becomes  more 
complex  and  results  in  putrefaction,  whereby  bad-smelling  gases 
are  evolved.  This  occurs  by  the  combination  of  the  carbon 
dioxide  with  the  ammonia  and  other  substances  to  produce  gases 
which  not  only  cause  much  offense,  but  are  undoubtedly  much 


226  REFUSE    AND  GARBAGE.  VI. 

more  injurious  to  health  than  the  products  of  decay  under  com- 
mon conditions. 

In  all  methods  of  the  disposal  of  garbage  the  aim  should  be 
to  remove  it  from  the  houses  at  frequent  intervals  and  before 
the  process  of  decay  has  fairly  begun,  and  to  deposit  it  under 
conditions  where  oxygen  mav  have  opportunity  to  attack  it  at 
every  part  so  that  putrefactive  decomposition  may  not  occur. 
In  a  village  this  may  often  be  successfully  done,  but  in  a  city 
it  is  practically  impossible.  Hence  other  methods  for  disposing 
of  garbage  have  been  developed,  namely,  methods  of  destruction 
by  fire  and  by  heat,  and  these  will  now  be  briefly  described. 

78.   CREMATION  OF  GARBAGE. 

The  method  of  disposing  of  garbage  by  burning  it  in  the  kitchen 
fire  is  one  that  has  long  been  practiced,  but  furnaces  for  the 
cremation  of  the  garbage  of  a  town  did  not  come  into  use  until 
after  1880.  Of  all  the  methods  for  destroying  decaying  sub- 
stances, that  by  fire  is  undoubtedly  the  most  effective,  as  thus 
all  accompanying  bacteria  are  killed,  and  the  organic  matter 
is  completely  oxidized  into  gases  and  only  ashes  are  left  behind' 
The  objections  to  the  method  are  two:  it  is  expensive,  and  it 
is  liable  to  produce  offensive  odors.  Both  of  these  objections 
have  been  gradually  diminished  by  the  experience  gained,  so 
that  since  1890  a  considerable  number  of  cities  in  Europe  and 
America  have  been  burning  their  garbage  and  street  sweepings 
with  economy  and  success. 

In  the  cremation  of  garbage  special  furnaces  lined  with  fire- 
brick are  employed,  and  a  cross-section  of  one  form  is  shown  in 
the  following  figure.  A  represents  the  furnace  chamber,  B  the 
ash  pit  below  the  grate,  E  one  of  the  openings  through  which 
the  garbage  is  dumped,  and  D  one  of  the  stoke  holes  through 
which  the  burning  matter  may  be  stirred.  The  width  ^of  the 
chamber  may  be  about  5  feet  and  its  length  about  15  or  20  feet. 


7&  CREMATION    OF   GARBAGE  227 

The  fuel  used  is  petroleum,  which  is  injected  through  pipes  at 
a  number  of  places  both  above  and  below  the  grate.  The  gaseous 
products  of  the  combustion  may  pass  to  the  end  of  the  chamber 
A  and  thence  into  a,  where  they  are  still  further  consumed  by 


SECTION  OF  GARBAGE  FURNACE. 

burning  oil.  The  disposition  of  the  gases  may  be  directly  into 
the  atmosphere  by  means  of  a  tall  chimney,  or  they  may  be  carried 
into  the  fire  under  a  steam  boiler  in  order  to  be  more  completely 
oxidized. 

Another  and  simpler  arrangement  is  to  use  both  the  furnaces 
A  and  a  for  burning  the  garbage,  the  gases  passing  up  a  common 
chimney.  Natural  gas  and  gas  made  from  bituminous  coal  have 
been  used  for  fuel  instead  of  petroleum.  In  the  early  furnaces  coal 
was  used,  but  this  requires  very  careful  stoking  in  order  to  main- 
tain the  high  degree  of  heat  necessary  for  effective  combustion. 
The  above  figure  gives  only  a  general  idea  of  a  crematory,  as 
the  details  of  arrangement  are  quite  different  in  the  furnaces 
of  different  patentees. 

The  process  of  cremation,  or  incineration  as  it  is  sometimes 
called,  was  employed  in  1906  for  about  180  towns  and  cities  in 
Great  Britain  and  to  a  less  extent  on  the  European  continent. 
In  America  it  was  first  used  in  1885  to  burn  the  garbage  at  army 
posts,  but  has  since  spread  widely;  prior  to  1906  twenty  different 
types  of  furnaces  were  patented  and  tried,  and  altogether  about 
125  garbage  crematories  had  been  put  into  operation,  some  of 
these  being  abandoned  after  a  short  period  of  service  on  account 
of  the  inefficient  combustion.  The  average  cost  of  burning 
one  ton  of  garbage  is  about  $1.00,  and  since  the  average  amount 
of  garbage  produced  in.  a  large  city  is  about  one-sixth  of  a  ton 


228  REFUSE    AND    GARBAGE.  VI. 

per  person  per  year,  a  rough  estimate  of  the  cost  of  garbage 
cremation  is  17  cents  per  person  per  year.  In  England  the  hot 
gases  from  the  crematories  are  widely  utilized  to  heat  boilers 
which  generate  power  for  pumping  and  electric-light  stations, 
so  that  a  portion  of  the  cost  of  the  fuel  is  saved  by  the  municipality. 
The  crematory  built  at  Marion,  O.,  in  1905  has  a  capacity 
of  30  tons  per  day.  Its  cost  was  $15  ooo,  and  it  is  operated  by 
two  men,  natural  gas  being  employed  as  a  fuel.  The  building 
is  40X40  feet  in  plan,  and  has  a  chimney  101  feet  high;  it  con- 
tains an  evaporating  floor,  a  stoking  room,  and  three  combustion 
chambers.  At  a  test  made  soon  after  its  completion,  eight  dead 
horses  were  thoroughly  reduced  to  ashes  in  five  hours  with  an 
expenditure  of  30  ooo  cubic  feet  of  gas  which  cost  1 5  cents  per 
thousand  feet.  This  crematory  burns  both  garbage  and  refuse. 

A  rubbish  incinerator  is  a  furnace  for  burning  the  combustible 
part  of  the  rubbish;  but  the  temperature  is  not  sufficiently  high 
to  burn  garbage.  The  rubbish  is  sometimes  dumped  upon  a 
wide  conveyor  belt  from  which  the  various  salable  and  metallic 
articles  are  taken  out  by  boys  who  stand  alongside  it.  Plants 
of  this  kind  have  been  installed  in  New  York,  Boston,  and  Buffalo 
with  satisfactory  results.  In  Europe  the  same  furnace  is  gen- 
erally used  for  burning  garbage,  street  sweepings,  and  rubbish. 
In  large  Ameiican  cities  the  tendency  has  been  to  have  a  special 
plant  for  garbage  cremation  in  which  no  other  refuse  is  burned, 
but  in  the  smaller  cities  the  three  classes  are  often  burned  in  the 
same  furnace.  Garbage  cremation  gives  the  greatest  offense  from 
escaping  odors  and  hence  the  plant  is  often  required  to  be  at 
some  distance  from  the  city  Since  1900  great  improvements 
have  been  made  in  obviating  this  source  of  complaint. 

79.    REDUCTION  OF  GARBAGE. 

The  term  reduction  or  digestion  is  used  for  a  method  of  garbage 
disposal,  first  used  about  1890,  in  which  the  garbage  is  heated 


79.  REDUCTION  OP  GARBAGE.  229 

by  steam  in  closed  vessels.  •  By  this  process  the  garbage  becomes 
separated  into  water,  grease,  and  solid  nitrogenous  matter.  The 
grease  is  utilized  in  the  manufacture  of  soap,  while  the  nitro- 
genous matter  contains  ingredients  which  render  it  useful  as  a 
fertilizer.  It  is  important  that  the  garbage  should  be  free  from 
ashes  and  metallic  substances  when  it  is  placed  in  the  reduction 
tanks.  The  method  is  one  for  treating  garbage  only,  and  is  not 
applicable  to  vegetable  rubbish  or  to  street  sweepings. 

A  reduction  tank  or  a  digestor  is  a  vertical  steel  boiler  which 
can  be  tightly  closed  by  a  cover  after  it  is  filled  with  garbage. 
To  this  tank  steam  pipes  are  attached,  through  which  steam 
is  forced  for  several  hours  and  thus  the  garbage  is  cooked  or 
digested.  This  cooking  produces  water,  which  falls  to  the 
bottom  of  the  tank,  and  lighter  nitrogenous  matter,  which  tends 
to  rise,  while  grease  is  mixed  with  both  of  these. 

The  arrangements  of  the  different  reduction  tanks  differ  in 
many  details.  A  common  form  is  about  6  feet  in  diameter  and 
20  feet  high,  the  upper  15  feet  being  cylindrical  and  the  lower 
5  feet  being  conical,  with  a  valve  at  the  bottom  for  drawing  off 
the  liquid.  The  garbage  is  dumped  into  the  top  of  the  tank  and 
rests  upon  a  grating  at  the  bottom  of  the  cylindrical  part.  The 
steam  is  then  applied  for  six  hours,  and  during  this  process  the 
waste  gases  and  steam  are.  carried  out  in  a  pipe  at  the  top  and 
condensed  in  a  water  tank.  The  liquid  matter  is  then  drawn 
out  at  the  bottom  of  the  cone  and  collected  in  vats,  where  the 
grease  rises  to  the  surface  and  is  skimmed  off,  while  the  remain- 
ing dark-colored  liquid  is  run  into  the  sewers.  The  more  solid 
matter,  called  tankage,  is  taken  out  at  a  door  just  above  the 
grating,  put  under  a  press  in  order  to  expel  the  water  and  grease 
still  remaining,  dried  in  ovens,  and  then  ground  into  powder. 

The  expense  of  construction  of  a  reduction  plant  is  greater 
than  that  of  a  crematory,  and  the  cost  of  disposal  per  ton  of 
garbage  is  about  double.  The  expectation  that  the  sale  of  the 
grease  and  tankage  would  be  sufficient  to  offset  this  disadvantage 


230  REFUSE   AND  GARBAGE.  VI. 

has  not  always  been  realized,  and  some  plants  have  been  aban- 
doned. The  method  is.  only  applicable  in  cities  where  there  is 
sufficient  garbage  collected  every  day  to  keep  a  plant  in  continuous 
operation.  Reduction  plants  have  generally  been  built  and 
operated  by  private  companies  with  the  hope  of  financial  return, 
and  about  twenty  were  in  use  in  the  United  States  in  1906.  The 
system  has  been  used  on  a  large  scale  at  Boston  and  New  York, 
the  plants  being  at  a  considerable  distance  from  the  cities  so  that 
complaints  regarding  offensive  odors  might  not  arise. 

The  largest  reduction  plant  ever  built  was  that  at  Barren 
Island,  about  27  miles  from  New  York,  where  the  greater  part  of 
the  garbage  of  New  York  City  was  treated  for  many  years  prior 
to  the  destruction  of  the  plant  by  fire  in  1906.  The  capacity 
of  this  plant  was  from  1000  to  1500  tons  of  garbage  per  day, 
this  being  towed  on  scows  from  the  collecting  yards  along  the 
water-front  of  the  city.  The  company  received  about  $120000 
per  year  from  the  city  for  towing  and  disposing  of  the  garbage, 
which  amounted  to  about  250  ooo  tons  per  year.  The  plant  had 
150  digesters,  each  of  10  tons  capacity  per  day,  with  numerous 
boilers,  presses,  and  dryers  for  treating  the  tankage  and  condensing 
basins  for  collecting  the  grease,  the  whole  covering  an  area  of 
about  six  acres.  During  the  construction  of  a  new  plant,  it  was 
necessary  for  New  York  to  resume  its  former  practice  of  dump- 
ing the  garbage  at  sea. 

Aside  from  offensive  odors,  almost  the  only  objection  to  the 
reduction  process  is  the  dark-colored  liquid,  which  is  often  run 
off  into  the  streams.  This  contains  much  organic  matter,  and 
although  the  bacteria  have  been  killed  by  the  cooking  and  boiling, 
others  will  soon  be  supplied  from  the  water  of  the  streatn,  and 
decay  will  then  take  place.  The  remedy  for  this  is  to  forbid  the 
introduction  of  such  liquids  into  rivers,  and  to  require  them  to 
be  purified  by  methods  of  chemical  precipitation  and  filtration. 
The  discharge  of  this  liquid  into  the  sea  at  a  point  far  removed 
from  the  city  is  less  objectionable. 


80.  ECONOMIC   CONSIDERATIONS.  231 


80.    ECONOMIC  CONSIDERATIONS. 

In  all  systems  for  the  disposal  of  house  and  street  refuse,  economy 
in  collection  and  in  final  disposal  is  a  matter  of  essential  importance. 
While  it  may  be  more  convenient  for  the  servants  of  a  household 
to  place  the  garbage,  ashes,  and  rubbish  in  one  receptacle,  this 
cannot  be  allowed  in  a  city  because  the  subsequent  disposal  of 
these  is  more  economical  when  they  are  kept  separate.  Ashes 
free  from  garbage  and  rubbish  often  have  a  value  for  filling  low 
lots  or  for  the  foundations  of  sidewalks,  or  sometimes  for  making 
concrete.  Garbage  mixed  with  ashes  or  rubbish  cannot  be  satis- 
factorily burned  in  crematories  or  be  treated  in  reduction  plants. 
Rubbish  mingled  with  ashes  or  garbage  has  some  of  its  salable 
articles  ruined.  Hence  the  convenience  of  servants  must  give 
way  to  the  economic  demands  of  the  municipality. 

In  the  disposal  of  garbage  by  burning  in  crematories,  the  escape 
of  hot  waste  gases  is  not  desirable  on  account  of  the  offense  that 
they  cause,  and  moreover  a  large  amount  of  heat  is  thus  lost. 
Numerous  efforts  have  hence  been  made  to  utilize  this  heat,  and 
in  England  great  success  has  been  attained  in  this  direction. 
Statistics  given  by  Goodrich  in  1901  mentioned  16  plants  the 
waste  gases  of  which  generated  nearly  2000  horse-powers,  this 
being  utilized  in  pumping  water  and  sewage  or  for  electric  power. 
On  the  average  about  2.4  horse-powers  were  obtained  by  the 
waste  gases  produced  in  burning  one  ton  of  refuse  per  day.  In 
the  United  States  this  economy  has  received  much  attention 
since  1900,  and  several  plants  have  attained  a  considerable  degree 
of  success.  Tests  made  by  Parsons  in  1905  at  one  of  the  rubbish 
incinerating  plants  in  New  York  indicate  a  higher  degree  of 
economy  in  utilization  than  that  above  mentioned,  and  show  that 
the  cost  to  the  city  is  materially  less  than  by  former  methods  of 
disposal. 

In  the  disposal  of  garbage  by  the  method  of  reduction,  the 
success  of  several  private  companies  indicates  that  they  derive 


232  REFUSE  AND  GARBAGE.  VI. 

a  profit.  These  companies  are,  however,  generally  paid  by 
the  city  for  hauling  or  towing  the  garbage  to  their  plants,  so 
that  economy  to  the  city  only  results  when  this  sum  is  smaller 
than  the  cost  of  other  methods  of  disposal.  A  municipality 
rarely  operates  a  reduction  plant,  for  the  process  is  one  for  the 
production  of  marketable  articles,  and  the  charter  of  a  city  gives 
it  no  power  to  carry  on  manufacturing. 

The  rubbish  collected  by  the  city  is  usually  sorted  over  in 
yards,  or  at  the  rubbish  incinerators,  by  contractors  who  pay  the 
city  for  the  privilege.  It  is  found  that  from  one-third  to  one- 
half  of  the  rubbish  consists  of  articles  which  have  a  market  value. 
In  1903  the  contractor  who  sorted  the  rubbish  in  the  boroughs 
of  Manhattan  and  Bronx  in  New  York  City  paid  $71  ooo  for 
the  privilege  of  removing  these  articles.  It  is  reported  that 
valuable  finds  of  jewelry  are  sometimes  made  by  the  boys  who 
sort  the  rubbish. 

The  street  sweepings  contain  fewer  constituents  of  value  than 
any  other  kind  of  refuse.  They  are  not  suitable  for  filling  low 
lots,  as  is  the  case  with  ashes,  on  account  of  the  organic  matter 
which  might  later  putrefy,  but  they  are  combustible  and  hence 
may  be  burned  in  incinerators.  New  York  City  loads  the  street 
sweepings  on  scows  and  dumps  them  at  sea,  as  is  also  done  with 
the  ashes.  While  the  street  sweepings  contain  a  good  deal  of 
manure  and  some  rubbish,  the  sorting  of  the  same  is  never 
profitable. 

The  various  systems  for  the  disposal  of  the  wastes  of  a  town 
have  now  been  briefly  described.  It  has  been  shown  how  fire, 
water,  air,  and  earth,  which  have  always  been  known  to  be 
effective  destroyers  of  decaying  organic  matter  in  small  quantities, 
may  be  applied  in  a  scientific  manner  to  the  disposal  of  the  refuse 
and  sewage  of  a  large  town.  The  manner  is  scientific  because 
the  reasons  are  known.  In  the  case  of  garbage  and  combustible 
refuse,  fire  changes  the  organic  matter  into  carbonaceous  gases 
and  mineral  substances.  In  the  case  of  sewage,  water  and  air 


8l.  ECONOMIC   CONSIDERATIONS.  233 

furnish  oxygen  by  which  the  bacteria  are  enabled  to  perform 
a  similar  decomposition,  and  water  and  air  acting  in  the  earth  do 
their  work  under  conditions  which  lead  to  no  offense.  The  pro- 
cesses which  man  has  found  most  effective  for  sewage  purification 
are  after  all  the  same  processes  that  nature  uses.  Dirty  water 
thrown  upon  sandy  ground  percolates  into  the  earth  and  ultimately 
a  part  of  it  becomes  pure  ground  water;  this  is  the  system  of 
intermittent  filtration.  Foul  water  thrown  over  a  cultivated 
field  percolates  and  is  absorbed  by  plants,  and  thus  a  part  of  it 
becomes  ground  water  and  another  part  becomes  living  organic 
matter;  this  is  the  system  of  broad  irrigation.  The  septic  tank, 
the  contact  bed,  and  the  continuous  sprinkling  filter,  are  methods 
by  which  man  attempts  to  hasten  the  processes  of  nature  and 
thus  secure  a  greater  degree  of  economy  than  can  be  obtained 
from  intermittent  filtration  or  broad  irrigation. 

Of  all  the  branches  of  engineering,  that  of  sanitary  work  is  the 
most  interesting  and  important.  It  is  interesting  by  reason  of  the 
physical  and  natural  sciences  that  are  constantly  to  be  studied  and 
applied,  and  because  of  its  wide  scope,  involving  as  it  does  the  co- 
operation of  the  physician,  the  chemist,  the  biologist,  the  hydrau- 
lician,  and  the  constructing  engineer.  It  is  important  because  it  is 
work  for  the  welfare  of  the  people,  and  has  its  influence  upon  all 
surrounding  communities  and  upon  the  nation.  The  city  engi- 
neer who  has  built  efficient  plants  for  water  supply  and  for  sewage 
removal,  or  who  has  instituted  efficient  methods  for  the  disposal 
of  refuse,  finds  satisfaction  of  a  high  degree  in  his  completed 
work,  for  thereby  the  public  health  is  promoted  and  the  world 
is  rendered  stronger  and  better. 

81.    EXERCISES  AND  PROBLEMS. 

74.  Consult  reports  of  the  State  Boards  of  Health,  and  ascertain 
the  details  of  two  or  three  cases  in  which  typhoid  fever  resulted  from 
the  pollution  of  wells  by  neighboring  privies. 

75  (a)  Consult  Parsons'  Disposal  of  Municipal  Refuse  (New 
York,  1906),  and  obtain  a  fuller  classification  of  city  wastes. 


234  REFUSE  AND  GARBAGE.  VI. 

75  W  Consult    Municipal    Engineering,    August,    1906,    and   obtain 
an  outline  of  the  method  used  at  Zerbst,  Germany,  for  the  purification 
of  wastes  from  slaughter  houses. 

76  (a)  Consult  reports  of  the  street  departments  of  different  cities, 
and  ascertain  the  cost  per  person  per  year  for  street  cleaning  and  ior 
the  disposal  of  the  sweepings. 

76  (b)  Consult   Hering's  paper   on   refuse   disposal,   read   before  the 
International  Engineering  Congress  of   1904.     (Transactions  American 
Society   Civil   Engineers,   vol.    54  E),   and   obtain   further  information 
regarding  the  composition  of  rubbish. 

77  (a)  Consult   Engineering   News,   November   5,    1903,   and   obtain 
statistics  regarding  the  different  methods    of    garbage  disposal  in  the 
United  States. 

77  (&)  Consult   Engineering   News  for   March    n,    1915,  and  obtain 
contract  prices  paid  by  the  City  of  New  York  for  the  removal  of  garbage, 
ashes  and  rubbish. 

78  (a)  Consult    Venable's    Garbage    Crematories    in    America    (New 
York,   1906)   and  make  sketches  showing  the  details  of  two  or  three 
different  types  of  furnaces. 

78  (6)  Consult   Engineering   Record,    August    18,    1906,    and   obtain 
a  description  of  the  refuse  destructor  at  Westmount,  Canada. 

79  (a)  Consult  Engineering  Record  for  November  19,  1910,  and  obtain 
facts  regarding  the  Columbus  garbage  reduction  plant. 

79(6)  Consult  Municipal  Journal  for  March  12,  1914,  and  find  facts 
regarding  the  Paterson  refuse  disposal  plant. 

80.  Obtain  facts  regarding  the  utilization  of  the  heat  of  refuse  incin- 
erators for  electric-light  plants  in  Chicago. 

81.  Consult  Engineering  News-Record,  October   25,   1917,  and  read 
Osborn's  article  upon  the  effect  of  the  war  in  garbage  production  and 
disposal. 


32.  NEW    WATER   SUPPLY   FOR   NEW   YORK   CITY.  235 


APPENDIX. 


82.  NEW  WATER  SUPPLY  FOR  NEW  YORK  CITY. 

The  boroughs  of  Manhattan  and  The  Bronx,  in  the  city  of 
Greater  New  York,  had  in  1900  a  population  of  2  050  600,  and 
in  1910  a  population  of  2  770  ooo.  About  95  per  cent  of  the 
water  consumed  in  these  boroughs  was  derived  in  1910  from  the 
Croton  watershed,  30  miles  to  the  northward,  the  area  of  this 
watershed  being  360  square  miles  and  the  greatest  supply  obtained 
from  it  in  dry  years  being  at  the  rate  of  336  million  gallons  per 
day.  The  consumption  of  Croton  water  in  these  boroughs 
increased  from  249  million  gallons  per  day  in  1900  to  301  million 
gallons  per  day  in  1905.  The  two  Croton  aqueducts  have  a 
combined  capacity  of  375  million  gallons  per  day. 

The  borough  of  Brooklyn  derived  its  supply  from  wells  and 
filter  galleries  in  the  ground  water  of  Long  Island  and  small 
surface  sources  which  were  insufficient  for  its  needs.  The 
boroughs  of  Queens  and  Richmond  were  inadequately  supplied 
by  several  private  companies.  The  imperative  necessity  of  pro- 
viding an  additional  water  supply  for  all  five  boroughs  of  the  rapidly 
growing  city  received  much  attention  since  1900  and,  after  many 
preliminary  studies,  a  definite  plan  was  adopted  in  1905. 

This  plan  provided  for  storage  reservoirs  to  impound  the  water 
of  several  streams  which  rise  in  the  Catskill  Mountains,  about 
100  miles  north  of  the  city.  The  capacity  of  these  reservoirs  was 
to  be  sufficient  to  furnish  an  average  supply  of  not  less  than  500 
million  gallons  per  day. 


236  APPENDIX.  82. 

The  Ashokan  reservoir,  impounding  the  waters  of  Esopus 
creek,  which  has  a  safe  yield  of  250  million  gallons  per  day,  was 
completed  in  1913.  It  has  an  available  storage  capacity  of  128 
billion  gallons,  or  sufficient  to  supply  the  city  for  250  days  at 
the  rate  of  500  million  gallons  per  day.  It  covers  an  area  of  about 
8000  acres  and  an  additional  7000  acres  surrounding  it  has  been 
purchased  to  secure  full  sanitary  control.  Several  villages  and 
many  miles  of  railway  and  highway  were  wiped  out  and  were 
required  to  be  moved  to  higher  ground.  From  this  reservoir  a 
large  aqueduct  has  been  completed  passing  southward  to  the 
Kensico  reservoir.  The  water  is  measured  as  it  leaves  the  Ashokan 
reservoir  and  again  both  when  it  enters  and  leaves  the  Kensico 
Reservoir  by  the  largest  Venturi  meters  ever  built.  They  are 
constructed  of  reinforced  concrete,  have  a  length  of  about  400 
feet  and  diameter  of  17.5  feet  with  a  throat  diameter  of  7.75  feet. 
The  inlet  and  throat  pressure  chambers  are  made  of  bronze.  The 
aqueduct  has  a  cross  section  area  of  241  square  feet  and  is  usually 
not  circular,  except  in  pressure  tunnels  and  pipe  lines.  Most 
of  the  so-called  cut  and  cover  work  lies  on  the  hydraulic  gradient 
and  is  constructed  of  reinforced  concrete,  the  cross  section  being 
a  horse-shoe  in  shape.  Where  the  aqueduct  falls  below  the 
hydraulic  gradient,  steel  pipe  encased  in  concrete  and  lined  with 
mortar  or  tunnel  in  rock,  lined  with  concrete,  is  used.  The  cross- 
ing of  the  Hudson  river  at  Cornwall  is  accomplished  by  a  tunnel 
bored  through  the  solid  rock  at  an  elevation  of  noo  feet  below 
the  level  of  the  river.  It  was  found  necessary  to  go  to  this  great 
depth  in  order  to  ensure  that  the  tunnel  would  be  in  solid  rock 
and  well  below  the  bottom  of  the  preglacial  Hudson  gorge.  The 
tunnel  is  connected  with  the  aqueduct  by  vertical  shafts  at  either 
end.  A  pumping  shaft  in  which  pumps  mounted  in  a  large 
float  can  be  placed  is  located  on  the  east  shore  of  the  river. 
These  pumps  and  float  follow  the  water  level  down  in  case  it 
should  ever  become  necessary  to  enter  the  tunnel  for  the  purpose 
of  making  repairs. 

A  new  reservoir  has  been  constructed  at  Kensico  on  the  old 


82.  NEW    WATER   SUPPLY   FOR   NEW   YORK   CITY.  237 

site  and  this  will  have  a  capacity  of  29  billion  gallons.  The  dam 
forming  this  reservoir  is  larger  and  higher  than  the  new  Croton 
dam,  being  307  feet  high  and  1825  feet  long;  it  contains  965  ooo 
cubic  yards  of  masonry.  The  aqueduct  is  carried  under  Man- 
hattan Island  by  a  tunnel  reducing  from  15  to  12  feet  in  diameter; 
it  lies  from  200  to  750  feet  below  the  surface  of  the  ground.  The 
tunnel  passes  under  the  East  River  to  Brooklyn,  this  being  u  feet 
in  diameter,  and  thence  branches  by  steel  pipe  to  supply  the 
boroughs  of  Brooklyn  and  Queens.  A  36-inch  cast-iron  pipe 
passes  under  the  Narrows  to  Staten  Island. 

The  total  length  of  the  aqueduct  from  the  Ashokan  reservoir 
to  its  terminals  in  Brooklyn  and  Staten  Island  is  126  miles,  dis- 
tributed as  follows:  cut.  and  cover,  51  miles;  grade  tunnel,  14 
miles;  pressure  tunnel,  35  miles;  pressure  aqueduct,  4  miles; 
steel  pipe  siphon,  6  miles;  and  pipe  conduit,  16  miles.  Connec- 
tions to  existing  mains  in  the  city  are  made  through  risers  from  the 
pressure  tunnel.  In  most  cases  pressure  regulators  will  be  placed 
on  these  so  as  to  reduce  the  pressure  to  that  desired  for  the  par- 
ticular area  to  be  served. 

Work  on  this  system  was  begun  in  1905  and  was  practically 
completed  in  1915.  Water  could  then  be  delivered  to  the  Croton 
aqueduct  in  case  of  an  emergency,  and  the  entire  system  was 
mostly  in  service  early  in  1917.  The  work  has  been  carried  on  by  a 
special  board,  created  for  that  purpose,  and  known  as  the  Board 
of  Water  Supply.  The  cost  of  this  work  was  approximately  $137- 
ooo  ooo,  not  including  the  development  of  the  Schoharie  water- 
shed, work  in  which  was  begun  in  1917. 

The  additional  250  million  gallons  per  day,  necessary  for  the 
full  capacity  of  the  aqueduct,  will  be  provided  by  diverting  the 
Schoharie,  and  creeks  though  a  tunnel  i8J  miles  long  to  the 
Ashokan  reservoir  from  whence  the  water  will  enter  the  aqueduct 
already  constructed.  This  system  when  complete  will  furnish 
New  York  with  a  water  supply  that  will  be  ample  for  its  needs 
until  1935. 


238  APPENDIX.  83. 

A  filter  plant  has  been  considered  in  connection  with  this  pro- 
ject to  be  constructed  south  of  the  Kensico  Reservoir  just  north 
of  the  city. 

83.  WATER  FILTRATION  IN  PHILADELPHIA 

The  population  of  the  city  of  Philadelphia  was  i  293  697  in 
1900  and  about  i  392  400  in  1904.  The  consumption  of  water 
in  1902  reached  the  high  figure  in  229  gallons  per  person  per 
day,  about  90  per  cent  of  the  same  being  derived  from  the  Schuyl- 
kill  and  10  per  cent  from  the  Delaware  River.  The  water  of 
the  Schuylkill  receives  much  pollution  from  manufacturing 
and  city  wastes,  and  the  consequent  high  death  rate  from  typhoid 
fever  in  Philadelphia  led  to  many  careful  studies  regarding  the 
purification  of  the  water  supply,  there  resulting  in  a  definite 
plan  for  which  $15  200  ooo  was  appropriated  in  1902,  while 
additional  appropriations  of  $6  800  ooo  were  made  in  1903  and 
1904,  and  a  further  sum  of  about  $5  ooo  ooo  was  needed  to  fully 
complete  the  work.  , 

The  system  as  now  constructed  and  in  operation  consists  of 
five  filter  plants,  using  the  slow  sand  method  of  filtration,  with 
several  sedimentation  and  distributing  reservoirs.  At  each  of 
these  plants  pumping  is  required  in  order  to  bring  the  water  to 
the  proper  height  for  distribution,  so  that  the  annual  expense  for 
operation  is  very  high.  Along  the  Schuylkill  river  there  are  three 
filter  plants,  known  as  the  Upper  Roxborough,  the  Lower  Rox- 
borough,  and  the  Belmont,  which  have  capacities  of  15,  13  and 
50  million  gallons  per  day.  The  other  two  plants  are  on  the  Dela- 
ware river  and  are  known  as  the  Torresdale  and  Queen  Lane; 
they  have  capacities  of  248  and  80  million  gallons  per  day.  About 
70  per  cent  of  the  city's  supply  is  now  obtained  from  the  Delaware 
and  30  per  cent  from  the  Schuylkill.  The  total  capacity  of  the 
five  plants  is  a  maximum  of  420  million  gallons  per  day,  sufficient 
to  filter  and  deliver  the  exceedingly  high  amount  of  230  gallons 
per  day  to  a  population  of  i  800  ooo. 


83.  WATER   FILTRATION   IN   PHILADELPHIA.  239 

The  plants  at  Upper  and  Lower  Roxborcngh  were  completed 
in  1903  and  that  at  Belmont  in  1904.  The  Torresdale  and  Queen 
Lane  plants,  owing  to  political  dissensions  and  legal  difficulties, 
which  arose  in  1905,  were  only  completed  and  capable  of  operating 
at  full  capacity  about  1913.  The  Philadelphia  filtration  system 
is  now  the  largest  in  the  world,  the  next  largest  being  that 
at  London,  where  214  million  gallons  per  day  were  filtered  in 
1902. 

The  three  plants  on  the  Schuylkill  are  arranged  in  the  same 
general  way.  Pumps  elevate  the  water  to  sedimentation  reser- 
voirs, from  which  it  passes  to  the  filter  beds,  and  thence  to  dis- 
tributing basins.  In  order  to  diminish  the  area  of  the  sand 
filter  beds,  preliminary  straining  of  the  water  through  sponge 
screens  is  provided  between  the  sedimentation  reservoirs  and 
the  sand  beds.  The  beds  are  covered  with  concrete  groined 
arches  in  order  to  render  their  operation  effective  in  the  winter 
season.  The  material  scraped  from  the  surfaces  of  the  beds  is 
removed  by  ejectors  to  the  sand-washing  apparatus.  From  the 
filtered  water  basins,  the  water  is  delivered  to  reservoirs  from 
which  it  flows  by  gravity  to  the  different  parts  of  the  city. 

At  the  Torresdale  plant  the  water  from  the  Delaware  River 
is  directly  delivered  to  the  filter  beds  by  low-lift  pumps  without 
sedimentation.  The  filtered  water  then  flows  by  gravity  a 
distance  of  nearly  three  miles  through  a  conduit  tunnel  to  a 
pumping  station  which  elevates  it  to  the  distributing  reservoirs 
This  tunnel  is  in  rock  along  the  bank  of  the  river  at  an  average 
depth  of  about  90  feet  below  the  surface  of  the  ground,  the  water 
passing  down  a  vertical  shaft  at  the  filter  plant  and  rising  through 
another  shaft  at  the  pumping  station.  The  shafts  and  tunnel, 
which  are  loj  feet  inside  diameter,  are  lined  with  brick,  this 
being  backed  with  concrete  so  as  to  fill  the  voids  between  rock 
and  brickwork.  This  tunnel  was  completed  in  1904  at  a  cost 
of  $i  350  ooo. 


240  APPENDIX.  84. 

84.  WATER  FILTRATION  AT  LITTLE  FALLS,  N.  J. 

While  not  the  largest  mechanical  filtration  plant,  that  at  Little 
Falls,  N.  J.,  was  the  first  large  plant  of  this  type  ever  constructed 
and  is  typical  of  all  of  the  other  plants  of  this  type  since  built  in 
the  United  States.  It  has  been  copied  and  referred  to  more  than 
any  other.  It  was  completed  in  1902  by  the  East  Jersey  Water 
Co.  It  filters  the  water  of  the  Passaic  River  which  is  supplied  to 
Paterson,  Passaic,  Montclair,  and  other  towns  in  eastern  New 
Jersey.  The  plant  was  designed  for  a  capacity  of  32  million  gal- 
lons per  day,  its  cost  was  nearly  $500,000,  and  the  cost  of  opera- 
tion is  about  $2.50  per  million  gallons  of  filtered  water. 

The  water  flows  from  the  river  through  a  canal  to  a  coagulating 
basin  where  alum  is  applied,  this  being  first  dissolved  in  small 
tanks.  From  that  basin  it  flows  to  the  filters,  which  are  rect- 
angular in  section,  each  15x24  feet  in  plan  and  13  feet  in  total 
height  above  the  lowest  drain.  The  depth  of  the  filtering  sand 
is  37  inches,  and  the  head  of  water  above  its  upper  surface  is 
about  6  feet.  For  controlling  the  rate  of  flow,  for  washing  the 
sand,  and  for  the  discharge  of  the  wash  and  clear  waters,  an 
elaborate  system  of  pipes  and  valves  is  provided.  In  the  washing 
air  is  first  blown  upward  through  the  sand,  and  this  is  followed 
by  an  upward  flow  of  filtered  water  until  the  wash  effluent  runs 
clear,  the  entire  process  taking  about  12  minutes. 

The  rate  of  flow  through  the  beds  is  usually  125  million  gallons 
per  acre  per  day,  or  nearly  thirty  times  as  great  as  that  used  in 
the  method  of  slow  sand  filtration.  The  percentage  of  the 
bacteria  removed  depends  upon  the  amount  of  coagulant  used, 
and  generally  ranges  from  95  to  98  per  cent.  The  amount  of 
organic  matter  removed  was,  in  1903,  about  38  per  cent  as 
measured  by  albuminoid  ammonia  and  .about  75  per  cent  as 
measured  by  oxygen  consumed.  The  bacterial  results  were  not 
,  materially  affected  by  higher  rates  of  filtration,  but  the  removal 
of  organic  matter  is  less  perfect.  The  temporary  hardness  of 
the  water  was  decreased  from  23  to  15  parts  per  million  by  the 


85.  THE   CHICAGO  DRAINAGE  CANAL.  241 

process,  but  the  permanent  hardness  was  increased  from  12  to 
19  parts  per  million.  All  turbidity  is  removed  and  the  filtered 
water  is  practically  colorless. 

85.    THE  CHICAGO  DRAINAGE  CANAL. 

The  city  of  Chicago  had  in  1890  a  population  of  r  099  850, 
which  had  increased  to  i  698  575  in  1900,  and  to  i  932  315  in 
1904.  Prior  to  1900  the  greater  part  of  the  sewage  of  the  city 
was  turned  into  Lake  Michigan,  from  which  the  water  supply 
is  derived  through  tunnels  extending  out  several  miles  to  the 
intakes,  and  as  a  consequence  the  death  rate  from  typhoid  fever 
was  high.  Plans  for  diverting  this  sewage  from  the  lake  had 
been  discussed  for  many  years  and  as  early  as  1861  a  small  part 
of  it  was  lifted  by  pumps  in  the  western  part  of  the  city  so  as 
to  discharge  it  into  the  Desplaines  River,  which  is  a  tributary 
of  the  Illinois  and  this  again  of  the  Mississippi.  A  definite  plan? 
adopted  in  1891,  provided  for  the  construction  of  a  canal  con- 
necting the  Chicago  and  Desplaines  rivers,  which  should  carry 
-sufficient  water  to  dilute  the  sewage,  this  water  being  obtained 
from  the  lake  by  reversing  the  direction  of  flow  of  the  Chicago 
River. 

Work  on  this  canal  was  begun  in  1892,  and  it  was  completed 
in  1900  at  a  cost  of  $33  ooo  ooo.  The  length  of  the  canal  is- 28 
miles,  the  depth  of  water  25  feet,  and  its  maximum  capacity 
nearly  10  ooo  cubic  feet  per  second,  a  volume  twenty  to  thirty 
times  as  great  as  the  sewage  of  the  city.  During  the  work  of 
construction  several  methods  for  the  excavation  and  removal  of 
earth  and  rock  were  developed  which  have  since  been  of  great 
value  to  the  engineering  profession. 

The  canal  had  been  in  operation  but  a  short  time  when  the 
State  of  Missouri  instituted  a  suit  in  the  Supreme  Court  of  the 
United  States  against  the  State  of  Illinois  to  restrain  its  further 
operation,  claiming  that  the  water  supplies  of  St.  Louis  and 
other  towns  on  the  Mississippi  below  the  mouth  of  the  Illinois 


242  APPENDIX.  86. 

River  were  endangered.  The  testimony  in  this  suit  fills  7975 
printed  octavo  pages,  embracing  that  of  35  technical  experts  as 
well  as  nearly  300  other  witnesses.  The  decision  of  the  court, 
rendered  in  1906,  was  to  the  effect  that  the  plaintiff  was  entitled 
to  no  remedy,  since  St.  Louis  had  neglected  to  take  preventive 
measures  against  sources  of  pollution  arising  in  Missouri  and 
since  the  claim  of  pollution  of  the  Mississippi  by  the  drainage 
canal  was  not  fully  established;  accordingly  the  bill  was  dis- 
missed without  prejudice. 

Other  interesting  problems  in  connection  with  this  canal  are 
those  of  furnishing  water  power  below  the  southern  terminus,  of 
the  widening  and  deepening  of  the  Chicago  River  which  will  be 
necessary  in  order  to  utilize  the  maximum  capacity  of  the  canal, 
and  of  its  possible  use  in  forming  a  part  of  a  navigable  water- 
way between  the  Great  Lakes  and  the  Mississippi  River. 

86.   BRITISH  COMMISSIONS  ON  SEWAGE  DISPOSAL. 

Several  important  reports  by  commissions  in  Great  Britain 
have  exerted  a  great  influence  on  the  development  of  efficient 
methods  of  sewage  disposal  and  utilization.  Probably  the 
marked  activity  in  England  which  resulted  in  developing  the 
septic  tank,  che  contact  bed,  and  the  sprinkling  filter  has  been 
caused  largely  by  the  public  demand  which  has  received  education 
through  the  work  of  these  royal  commissions.  The  first  one, 
appointed  in  1843,  made  inquiries  regarding  the  best  means  to 
improve  the  health  of  towns;  the  second,  appointed  in  1857,  dealt 
with  sewerage  and  sewage;  the  third,  constituted  in  1869,  treated 
the  subject  of  river  pollution;  and  the.fourth,  appointed  in  1898, 
and  the  fifth,  now  at  work,  have  had  under  discussion  the  entire 
subject  of  sewage  disposal.  The  reports  of  these  commissions 
to  parliament,  published  in  the  so-called  blue  books,  contain  the 
testimony  of  many  technical  experts,  as  also  valuable  summaries 
of  each  branch  of  the  subject  and  important  conclusions.  The 
studies  of  the  last  commission  have  embraced  bacteriological  as 


87.  EXERCISES   AND  PROBLEMS.  243 

well  as  chemical  investigations,  and  also  the  details  of  operation 
of  the  different  systems  of  sewage  disposal.  The  reports  of  the 
commissions  are  primarily  intended  to  give  information  to  par- 
liament that  will  serve  as  a  guide  for  the  enactment  of  laws  to 
promote  the>  public  health,  and  hence  deal  with  the  subject  from 
a  slightly  different  point  of  view  than  that  of  the  engineer;  never- 
theless they  contain  much  matter  of  value  to  all  engaged  in 
sewage  disposal,  and  have  exerted  a  marked  influence  on  the 
progress  of  this  important  branch  of  sanitation. 

% 
87.    EXERCISES  AND  PROBLEMS. 

In  the  following  exercises  references  to  journals  are  not  given, 
but  it  is  intended  that  the  student  shall  consult  indexes  to  engi- 
neering literature  and  ascertain  the  references  for  himself.  The 
Engineering  Index,  issued  prior  to  1892  by  the  Association  of 
Engineering  Societies  and  later  by  the  Engineering  Magazine, 
will  be  found  useful  for  this  purpose:  Vol.  I  embraces  the  years 
1884-1891,  Vol.  II  the  years  1892-1895,  Vol.  Ill  the  years  1896- 
1900,  Vol.  IV  the  years  1901-1905  and  thereafter,  one  volume  for 
each  year. 

2  (d)  Give  facts  concerning  the  plague  which  swept  over  London  in 
1665. 

3  (c)  What  important  discovery  was  made  early  in  the  twentieth  cen- 
tury regarding  the  prevention  of  yellow  fever? 

4  (c)  Which  twenty  cities  of  the  United  States  had  the  highest  death 
rates  from  typhoid  fever  in  the  years  1910  to  1914? 

ii  (c)  What  is  meant  by  the  alkalinity  of  water,  and  how  is  it  deter- 
mined and  expressed?  What  degree  of  alkalinity  renders  a  water  un- 
suitable for  drinking? 

13  (c)  Find  comparative  analyses  of  influent  and  effluent  for  several 
of  the  larger  filter  plants  in  the  United  States. 

1 6  (c)  What  place  in  the  world  has  the  greatest  annual  rainfall  and 
how  much  is  it? 

17  (c)  Obtain  facts  regarding  rainfall  on  the  Pacific  Coast  of  North 
and  South  America. 


244  APPENDIX.  87. 

21  (c)  Ascertain  the  number  of  reservoirs  on  the  Ashokan  supply  of 
New  York  City,  with  the  location  and  capacity  of  each. 

27  (b)  Describe  and  obtain  sketches  of  the  mechanical  filtration  plant 
completed  in  1915  at  Baltimore,  Md. 

28  (d)  Describe  the  slow  sand  filtration  plant  completed  in  1906  at 
Washington,  D.  C.,  especially  the  methods  for  cleaning  the  beds  and 
washing  the  sand. 

29  (c)  Give  accounts  of  the  slow  sand  filtration  plants  at  Berlin  and 
Altona,  Germany. 

29  (d)  Find  costs  of  operation  and  maintenance  of  several  filter  plants 
in  the  United  States. 

29  (e)  Find  the  cost  oi  operating  the  Cincinnati  filtration  plant  for 
each  of  the  six  years  ending  with  1914. 

31  (6)   Give  brief  descriptions  of  the  water-supply  systems  of  Louis- 
ville, Ky.,  and  of  Minneapolis,  Minn. 

32  (6)  Show  a  comparison  of  the  consumption  of  water  in  cities  where 
services  are  unmetered  with  those  where  services  are  metered. 

35  (d)  Obtain  a  diagram  of  the  cross  section  of  the  new  Croton  dam, 
showing  the  principal  dimensions. 

35  (e)  Obtain  facts  concerning  some  of  the  more  recent  dam  failures. 

35  (/)  Obtain  sketches  of  the  reinforced  concrete  dam  completed  in 
1913  at  Guayabal,  Porto  Rico. 

37  (ft)  Find  facts  concerning  the  aqueduct  for  the  city  of  Los  Angeles, 
Cal. 

40  (6)  Obtain  information  regarding  the  pumping  plants  for  pumping 
the  water  from  the  Rondout  and  Hudson  siphons  of  the  Catskill  Aqueduct. 

44  (d)  Describe  the  water  tank  built  at  East  Providence,  R.  I.,  in 
1904,  and  that  which  failed  at  Fairhaven,  Mass.,  in  1901. 

50  (c)  Describe  the  topography  of  New  Orleans,  La.,  and  give  some 
account  of  its  sewerage  and  drainage  systems. 

53  (e)  Describe  the  new  sewerage  system  of  the  city  of  Baltimore,  Md. 

63  (c)  Give  accounts  of  the  suits  regarding  the  pollution  of  the  Nassau 
River  and  of  the  Kennebec  River  by  the  sewage  of  towns. 

69^1  (6)  Give  a  list  of  some  of  the  more  important  installations  of 
Imhoff  tanks  in  the  United  States. 

72  (c}  Give  an  account  of  the  operation  of  sewage-disposal  plants 
in  Ohio,  Illinois,  and  Wisconsin  during  the  winter  of  1904-1905. 

80  (6)  Describe  the  methods  of  garbage  collection  and  disposal  used 
at  Milwaukee,  Wis.,  Pittsburg,  Pa.,  and  Washington,  D.  C. 


87.  EXERCISES   AND  PROBLEMS.  2440 

82.  Discuss  one  or  more  of  the  following  topics  regarding  the  new 
water  supply  of  the  city  of  New  York:  (a)  Rainfall  and  evaporation 
in  the  Catskill  region;  (b)  Proposed  filtration  of  the  Catskill  water; 
(c)  Character  of  the  ground  water  of  Long  Island. 

83  (a)  Draw  a  map  showing  the  filtration  plants  and  distributing 
reservoirs  of  the  city  of  Philadelphia. 

83  (b}  Obtain  sketches  showing  the  arrangement  of  the  Belmont 
filtration  plant  in  Philadelphia. 

83  (c)  Obtain  sketches  and  facts  regarding  the  construction  of  the 
Torresdale  conduit  tunnel. 

84  (a)  Draw  a  map  showing  the  topography  of  Chicago  and  vicinity, 
especially  the  lake  front,  the  river,  and  the  drainage  canal. 

84  (b)  Give  facts  regarding  the  transmission  of  Bacillus  prodigiosus 
from  Chicago  to  St.  Louis  through  the  drainage  canal  and  rivers. 

85.  Obtain  a  sketch  showing  the  arrangement  of  the  mechanical 
filter  plant  at  Little  Falls,  N.  J. 

87  (a)  Give  an  account  of  the  results  attained  at  Havana,  Cuba, 
since  1899,  through  sewerage  and  sanitation. 

87  (6)  Give  an  account  of  the  sanitary  work  done  along  the  line  of 
the  Panama  Canal  since  1904,  and  state  some  of  the  results  that  have 
been  thereby  secured. 

87  (c)  Read  the  discussions  on  advance  in  sewage  disposal,  held  at  the 
annual  convention  of  the  American  Society  of  Civil  Engineers  in  1906, 
and  especially  note  the  classification  of  methods  given  by  Whipple. 

87  (d)  Find  facts  regarding  rat  suppression  for  the  prevention  of 
bubonic  plague. 

87  (e)  Give  some  account  of  the  exercises  held  in  New  York  on  October 
12-14,  1917,  to  celebrate  the  formal  introduction  of  the  Catskill  water 
into  the  city. 


INDEX. 


245 


INDEX. 


Aeration  of  filter  beds,  82,  195 

sewage,  187,  206,  209 
water,  63,  112 

Aerobic  bacteria,  21,  180 

Air,  composition  of,  26 
in  sewers,  166 

Air  inlet,  157 

lift  pump,  115 

Albuminoid  ammonia,  32,  35 

Algae  in  water,  37 

Alum  in  precipitation,  70,  189,  239 

Aluminum,  72 

Ammonia,  22,  32,  35,  225 

Anaerobic  bacteria,  21,  180,  202 

Analyses  of  sewage,  41,  181,  197,  210 
water,  41,  65,  68,  76,  80 

Analysis,  biological,  36,  39 
chemical,  33,  39 

Anderson's  purifier,  77 

Anrrual  rainfall,  50 

Aqueducts,  10,  103,  104,  106 

Arched  culverts,  103 

Archimedean  screw,  170 

Artesian  wells,  59,  60 

Ashes,  disposal  of,  220 

Assessments  for  sewers,  175 

Babylon,  reservoirs  of,  9 

Bacillus  coli  communis,  33,  185,  211 

Bacteria,  18,  23,  38,  40,  180 
classification,  19 
in  sewage,  181,  186,  204 
in  water,  38,  41,  80 

Bacteriological  analyses,  36,  37,  40 

Bacteriology,  18 


Bail  trap,  143,  172 

Baltimore,  Md.,  212,  215 

Bell  trap,  143 

Berlier's  evacuator,  172 

Berlin,  sewage  farms,  201 

Bethlehem,  Pa.,  water  works,  87 

Black  death,  10 

Boards  of  health,  15,  25,  184 

Boiler  for  kitchen,  133 

Boiling  of  water,  60 

Boston,  Mass.,  sewage  disposal,  169 

water  works,  87 
British  commissions,  241 
Broad  irrigation,  198,  212 
Brockton.  Mass.,  sewage  filtration,  i< 
Bromine  as  disinfectant,  113 
Brook  water,  55 
Brooklyn,  N,  Y.,  watdr  supply,  58 

Canals,  103 

Capacity  of  reservoirs,  91,  93 

Cast-iron  pipes,  107,  129 

Catch  basins,  155 

Catskill  reservoirs,  235 

Centrifugal  pumps,  115,  169 

Cesspools,  53,  141,  202,  216 

Champaign,  111.,  septic  tank,  204 

Charcoal,  72,  198 

Charleston,  S.  C.,  artesian  wells,  59 

Chemical  analysis,  33,  36 

precipitation,  70.  188,  222 

Chicago,  drainage  canal,  240 
sewerage,  169,  240 
water  supply,  56,  125 

Chloride  of  lime,  71,  217 


246 


INDEX. 


Chlorine,  33,  39,  57,  67,  716,  196 
Cholera,  24,  28,  40 

at  Hamburg,  29 
at  Manila,  24 
Cisterns,  53,  54 
Civil  engineering,  8 
Clark's  softening  process,  69 
Cleaning  of  cesspools,  217 
cisterns,  54 
filter  beds,  81,  196 
sewers,  165 
streets,  221 

Cloaca  maxima,  140,  162 
Coal,  117,  119 

Coefficients  for  aqueducts,  105 
pipes,  109 
sewers,  169 
Coke,  73,  169,  185 
Collecting  reservoirs,  60,  61 
Collection  of  water  samples,  33 
Columbus,  O.,  sewage  disposal,  193,  204^ 

208,  210,  213 
Combined    system    of    sewerage,    151, 

167,  175 
Concrete  dams,  100 

foundations,  163 

sewers,  164 
Conduits,  104,  190 
Consumption,  13,  17 
Consumption  of  water,  10,  89 
Contact  beds,  205,  212 
Contagious  diseases,  14 
Continuous  filtration,  82,  209 
Copperas,  189 
Core  of  a  dam,  94 
Covered  filter  beds,  82 
reservoirs,  62 

Cremation  of  garbage,  226,  231 
Croton  aqueducts,  106,  236 
Culture  for  bacteria,  38 
Culverts,  103 

D  trap,  143 

Damascus  water  supply,  140 

Dams,  earthen,  94 


Dams,  masonry,  97 
Danzig,  typhoid  fever  at,  24 
Death,  black,  10 
Deaths  in  1900,  in  U.  S.,  17 

registration  of,  15 
Decay  of  garbage,  224 

organic  matter,  22 
Decomposition  of  sewage,  180 
Deep  wells,  59 
Deodorizers,  217 
Depew,  N.  Y.,  coke  beds,  207 
Deposits  in  reservoirs,  112 

sewers,  154,  161 
Desmids  and  diatoms,  37 
Digestion  of  garbage,  229 
Diphtheria,  17 

Direct  pumping,  88,  122,  125 
Disease  and  air,  25 
filth,  23 
water,  28 

Diseases,  classification  of,  12 
germs  of,  20 
zymotic,  14,  17 
Disinfectants,  217 
Disk  meter,  133 
Disposal  of  garbage,  224-232 
sewage,  180-214 
sludge,  191,  204 
Dissolved  matter  in  water,  31 
Distillation  of  water,  68 
Distributing  reservoirs,  62,  no,  113 
Double-acting  pump,  114 
Drainage  of  houses,  146 

soil,  152,  163 
Drain  pipes,  148,  195 
Driven  wells,  58 
Duplex  pump,  114 
Duty  of  pumping  engine,  117 

Earth  closet,  141 

dams,  94,  95 

East  Jersey,  N.  J.,  conduit,  107 
East  Orange,  N.  J.,  filter  beds,   197 
Economic  considerations,  118,  231 
Electrical  purification,  70,  85,  210 


INDEX. 


247 


Endemic  diseases,  14 
Epidemic  diseases,  14 
Epidemics,  black  death,  10,  24 

cholera,  22,  29 

typhoid   fever,  24,  28,   29, 

84,  216 

Evaporation,  51 
Exeter  septic  tank,  203 

Factories,  wastes  of,  182 
Failure  of  dams,  96 

standpipes,  128 
Farms,  sewage,  198,  201 
Filter  basin,  67 

beds,  78,  80,  83,  113,  195,  209 
galleries,  67,  85 
Filters,  household,  72 

mechanical,  70,  75 
Pasteur,  73 
sprinkling,  209,  213 
Filth  and  disease,  23 
Filtration,  continuous,  82,  209 
intermittent,  82,  194 
mechanical,  239 
natural,  66,  212 
slow  sand,  77,  85,  237 
Fire  hose,  130 
pressure,  130 
service,  90 
streams,  131 

Flies,  disease  spread  by,  216 
Flush  tanks,  134,  158 
Foundations,  97,  162 
Free  ammonia,  32,  35 
Friction  in  pipes,  109,  121 
Frost  protection  for  hydrants,  130 

dams,  95 
Furnace  for  garbage,  227 

Galleries  for  filtration,  67,  85 
Garbage,  collection  of,  141,  219,  224 
cremation  of,  226,  231 
decay  of,  224 
reduction  of,  228,  231 
GaseB  in  sewage,  166,  202 


Gases  in  water,  31 
Gate  chambers,  103,  112 
Germs  of  disease,  13,  19 
Gravity  sewerage  systems,  151 

water-supply   systems,  86,  92, 

"3 

Grease  trap,  144 
Ground  water,  52,  57,  58 

Hamburg,  cholera  at,  29 

filter  beds  of,  85 
Hand  hole  in  pipes,  157 
Hard  water,  32,  69 
Hardness,  scale  of,  34 
Health,  6,  12 
Heisch's  test  of  water,  38 
Historical  notes,  9,  139 
House  drainage,  146,  147 

filters,  72 

fixtures,  143 

meters,  133 

pipes,  132 

refuse,  219,  221 
Hydraulic  grade  line,  108 
radius,  105,  108 

Hydraulics,  101,  105,  108,  121,  160 
Hypochlorite,  710 

Imhoff  tank,  205 
Impure  air,  25 

water,  28 

Incinerators,  227,  228 
Infectious  diseases,  14 
Influenza,  14 

Intermittent  filtration,  82,  194,  212 
Interpretation  of  analyses,  39 
Iron  perchloride,  71 

precipitation  by,  71,  77,  201 

spongy,  73 
Irrigation,  60,  209 

Jerusalem,  aqueducts  of,  9 
Johnstown,  Pa.,  failure  of  dam,  96 

Karcha,  cisterns  of,  9 


248 


INDEX. 


Kitchen  boiler,  134 

sink,  134,  144 

Lake  water.  56 

Lamp  hole,  157 

Laundry  fixtures,  134,  144 

Lawrence,  Mass.,  filter  beds,  82 

typhoid  fever,  79 
Lead  pipes,  133 
Liernur's  sewerage  system,  171 
Lime,  69,  71,  188 
Limewater,  69 
London,  covered  reservoir,  62 

drains,  n 

mortality  of,  18,  24 

sewerage,  141 
Los  Angeles,  Cal.,  201 

Malaria,  13,  14,  26 
Manholes,  155,  157,  166 
Manila,  cholera  at,  24 
Marion,  O.,  207,  228 
Masonry  dams,  98 

for  sewers,  163 
Mechanical  filters,  70,  74 
Median  age  of  population,  43 
Memphis,  Tenn.,  sewers,  156,  178 
Missouri  river  water,  63 
Mortality,  rate  of,  15,  16 

Natural  filtration,  66 

New  York,  aqueducts,  106,  236 
garbage  disposal,  230 
harbor,  211 
new  water  supply,  235 
reservoirs,  no,  236 
water  consumption,  93,  235 

Nitrates,  22,  33,  36 

Nitrification,  23,  36,  181 

Nitrites,  33,  185 

Nitrogen  as  nitrates  and  nitrites,  36 

Organic  matter,  21,  23 
Overflow  sewers,  154 
Oxygen,  n,  20,  26,  31 
consumed,  36 


Ozone,  72 

Pail  system  of  removal,  141 
Paris,  covered  reservoirs,  62 
sewage  farms,  201 
sewers,  142 
Pasteur  filter,  73 
Penstocks,  167 
Percolation,  51 
Permanent  hardness,  32 
Philadelphia,  water  filtration,  237 
Pipes,  106,  107,  129,  133 
friction  in,  121 
house,  132 

thickness  of,  121,  127 
Piston  meter,  133 
Plants,  growth  of,  22 
Pneumatic  cart,  218 
Pollution  of  reservoirs,  113 

rivers,  56, 181, 183 
Potassium  permanganate,  71 
Precipitation  of  sewage,  188 

water,  70,  77 
Pressure  in  pipes,  91,  131 

regulator,  131 
Privies,  141,  216 
Pullman,  III.,  sewage  farm,  201 
Pumping,  direct,  122 

of  sewage,  151,  168,  170 
to  reservoir,  120 
to  standpipe,  124 
to  tank,  123 
Pumping  engines,  116 
Pumps,  113 
Purification  of  garbage,  225 

sewage,  180-215 
water,  47—82 
Purity,  standards  of,  40 
Putrefaction,  205,  225 

Rainfall,  47,  148 
Rain  gage,  47,  84 
water,  52,  53 

Rate  of  filtration,  78,  194 
mortality,  16 


INDEX. 


249 


Reading,  Pa.,  sewage  filtration,  188 

water  supply,  64 
Reduction  of  garbage,  228,  231 
Refuse  of  towns,  216-242 
Regulation  of  pressure,  131 
Removal  of  garbage,  63,  224 

refuse,  220 
Reservoir  dams,  94,  97,  TOO 

embankments,  94,  112 
Reservoirs,  ancient,  60 

distributing,  62,  86,  no 
pumping,  2,  120 
storage,  61,  86,  236 
River  pollution,  56,  183 

water,  55,  183 
Rivers,  purification  of,  185 
Rochester,  reservoir,  62 

water-pipe,  107 
Rome,  aqueducts,  10 

sewers,  140 
Rotary  meter,  133 

sprinkler,  210 
sweeper,  223 
Rubbish,  219,  228,  232 
Runoff,  51 

S  trap,  143 

Sand  for  filter  beds,  81 

Sanitary  code,  9,  44 

engineering,  9,  12,  233 

science,  7-42 
Schuylkill  river,  185 
Scraping  streets,  222 
Screens,  72,  169,  185,  187,  197 
Sedimentation,  63,  84 
Separate  system  of  sewerage,  151,  156, 

167 
Septic  sewage,  181,  195 

tanks,  202,  212 
Sewage,  139,  180-215 

aeration,  187,  2096 

analyses,  41,  181,  197,  210 

farming,  199,  201 

filtration,  194,  199 

precipitation,  188 


Sewage,  pumping,  168,  171 

screening,  169',  185,  187 
sterilization  of,  211 
Sewage  systems,  139-178 
combined,  152 
separate,  156 
vacuum,  170 
Sewer  gas,  155,  1 66 
Sewers,  ancient,  140 

cleaning  of,  165 

construction  of,  162 
'  sizes  of,  159 

ventilation  of,  162 
Shone  system,  173 
Silt,  31,  63 

Single-acting  pump,  162 
Siphon  flush  tank,  159 
Slopes  of  sewers,  160 
Sludge,  191,  193 
Smallpox,  n,  14 
Snow,  54 

Sodium  chloride,  32 
Softening  of  hard  water,  69 
Soil  pipe,  146 
Spongy  iron,  73 
Spring  water,  57 
Springs,  57,  60,  216 
Sprinkling  filters,  209   211 
Stale  sewage,  181,  195 
Standards  of  purity,  40 
Standpipes,  124,  126,  127 
Steam  engines,  117 
Storage  of  sewage,  186 

water,  63 

reservoirs,  60,  91,   103,  107 
Strainers,  72,  185 
Street  cleaning,  221 
dust,  26,  221 
mains,  129 
pavements,  222 
refuse,  220 
Suction  pump,  113 
Sunlight,  action  on  bacteria,  20 
Surface  water,  54 
Suspended  matter  in  water,  30 


250 


INDEX. 


Swamp  water,  55 
Sweeping  streets,  223 

Tables,  list  of: 

Aqueducts,  105 

Deaths  in  U.  S.,  17 

Median  ages,  43 

Pipes,  109,  121 

Pumping  engines,  118 

Rainfall,  50 

Sewers,  160 

Tank  reservoirs,  123,  126 
Tankage,  229 

Tanks  for  precipitation,  191 
Temporary  hardness,  32 
Thickness  of  dams,  98 

pipes,  121,  127 
Tilting  flush  tank,  159 
Topography,  92,  153 
Torresdale  conduit,  239 

filjter  plant,  238 
Total  solids  in  sewage,  150,  180 

water,  34 

Traps,  143,  146,  1 66 
Triplex  pump,  114 
Tuberculosis,  13,  26 
Typhoid  fever,  cause,  13,  20,  28,  183 
deaths  from,  17,  79 
epidemics,  13,  28,  216 
Typical  analyses,  41 

Vaccination*  n,  14 


Vacuum  pump,  113 

Vacuum  systems  of  sewerage,  151,  170 

Vaults  for  filter  beds,  82 

Velocity  in  pipes,  109 

in  sewers,  161 

of  sedimentation,  63 
Vent  tube,  147 
Ventilation  of  houses,  27 
sewers,  166 
streets,  27 
Venturi  water  meter,  132 

Washington,  D.  C.,  220,  244 

Waste  weirs,  97,  101 

Water,  analyses,  41,  65,  68,  76,  80 

biological  analysis,  37,  39 

chemical  analysis,  33,  39 

closets,  134,  145 

consumption  of,  89 

matter  in,  30 

meters,  132 

purification,  47-85 
Watershed,  51,  92,  102 
Water-supply  systems,  86-138 
Water  works  in  U.  S.,  88 
Wells,  58,  59,  88,  217 
Wetted  perimeter,  105 
Williamsburg,  Mass.,  dam  failure,  96 
Worcester,  Mass.,  sewage,  192,  197 
World's  Fair,  sewerage  of,  174,  192 

Zymotic  diseases,  13,  17,  24,  28,  37 


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